We have 2 questions (this one and this one) that are asking for answers to homebrew up a class for them.
To me this seems like it's both very broad and entirely opinion-based. I can't see a way to judge answers objectively. Since there's 2 of them, I figured it was worth checking with meta.
Are these questions an acceptable fit for this site?
There are three hurdles that must be passed in my mind:
I agree with @BrianBallsunStanton's answer, and believe that these two questions can be a fit for the site given those criteria.
The questions are pretty specific about the exact attributes they want the resulting class to have (feels like the 4e avenger in that it uses giant sword, but can Turn Undead and isn't STR-based).
There are rules/guidelines for class creation in the 5e DMG
An answer doesn't have to be an entire 3 page class writeup, it's OK for answers to be more general in proportion to broadness of question (for example, questions on "in general how do I emulate a specific genre well in my game" and "how do I emulate the pirate genre in my game" are both on topic, it's just that genre-emulation 101 info is appropriate for the first as an answer and highly detailed pirate things are appropriate for the second).
Therefore these questions should be answerable by someone who has specifically tried to emulate those older classes in 5e. Now, this means that maybe they won't get answered quickly - they should not be answered by someone who just does some theory work and says "Oh, it seems to me that should play like the Avenger", it should be answered by someone who's actually played to get that "avenger feel" in 5e - but "not likely to be answered" is not a site criteria for question validity. This does mean that even the OP's answer to the Invoker question is invalid until tried in play and it results in either acceptable invoker simulation or not. If the requirements were made purely technical (class must use large weapon and turn undead and have STR < 15) then it could be answered from a rules theory perspective, if they are somewhat subjective (plays like the avenger, feels like divinely guided) then it requires play to be Good Subjective. However, given that, it's not less answerable than any technique question that's not "get my DPS to 20."
I don't feel any content commission questions are appropriate for the site...
Opening the door for homebrew commission questions is asking for a whole world of trouble. As you state there is no way for the community itself to effectively vote up or down on answers submitted to these type of questions. The lenght of answers for this type of question would be long by necessity (the final version of a class usually takes up 1 -2published pages). Further this makes a foundation for letting other type of commission/submission request questions into the site.
To me this seems like it's both very broad and entirely opinion-based. I can't see a way to judge answers objectively.
I don't feel at all like they are entirely opinion based and I see many ways of how to objetively judge the questions.
Examples:
Is there a way to emulate/simulate the 4e Archer Ranger in 5e?
Yes. Use the 5e fighter with Archery Style. Since the ranger in 4e is a martial class. It doesn't give you the feeling of much more than a well trained archer. You can use a background to fulfill the lore side of a nature strider.
Is there a way to emulate/simulate the 3.5e Arcane Archer in 5e?
Yes. Use the 5e Eldritch Knight with Archery Style. It will allow you to be good with the bow and have a spell list
Is there a way to emulate/simulate the Rune Priest in D&D 5e?
Yes. The simple way is this: go for a melee Eldritch Knight, change the spellcasting Ability to WIS and, instead of using the Wizard Spell List, use the Cleric Spell List. Being the case, you'll have enough divine power to feel like you're using rune-magic and will manage to handle yourself in close combat very well, just like a Rune Priest would
Not all the answers are going to be short, though. And it's not entirely opinion based. Besides having to know what makes the class itself tick (as in, Invokers being intuitive casters, Avengers having their swords guided by their gods, Runepriests being a tanky-battle-cleric with a limited divine power), you have to follow what the DMG considers correct when doing those changes. Check what the 5e Dungeon Master's Guide says, Page 288:
The first step is to figure out what class feature or group of class features you're going to replace. Then you need to evaluate what each feature provides to the class, so that the features you are adding don't make the class over- or underpowered. Ask yourself the following questions about a feature you're replacing:
What impact does replacing the feature have on exploration, social interaction, or combat?
Does replacing the feature affect how long the party can continue adventuring in a day?
Does the feature consume resources provided elsewhere in the class?
Does the feature work all the time, or is it regained after a short rest, a long rest, or some other length of time?
The answers in the Invoker's issue respect all of these. Including the change made in the spell-list that was suggested for when you use the Sorcerer or Wizard as a guideline. The DMG goes further:
CHANGING PROFICIENCIES (DMG 287)
Changing a class's proficiencies is a safe and simple way to modify a class to better reflect your world. Swapping out one skill or tool proficiency for another doesn't make a character any stronger or weaker, but doing so can change the flavor of a class in subtle ways. For example, a prominent guild of rogues
The designers are saying this is a good solution, and it's used in my answer when suggesting the Invoker should use Staffs and Rods as spell foci.
When it comes to changing other things in the design (like what I asked about the Avenger in one of those questions, we go here:
SUBSTITUTING CLASS FEATURES (DMG, Page 287)
If one or more features of a given class don't exactly fit the theme or tone of your campaign, you can pull them out of the class and replace them with new ones. In doing so, you should strive to make sure that the new options are just as appealing as the ones you are removing, and that the substitute class features contribute to the class's effectiveness at social interaction, exploration, or combat just as well as those being replaced.
And when it's about making a new spell list for the class (as suggested in the Runepriest example or in my answer for the Invoker's problem), here is what the DMG has to say about it:
CHANGING SPELL LISTS (DMG, page 287)
Modifying a class's spell list usually has little effect on a character's power but can change the flavor of a class significantly. In your world, paladins might not swear their oaths to ideals, but instead swear fealty to powerful sorcerers. To capture this story concept, you could build a new paladin spell list with spells meant to protect their masters, drawn from the sorcerer or wizard lists. Suddenly, the paladin feels like a different class.
As a matter of fact, checking all of this, the answer that I left for the Invoker should have been even longer, honestly. I should have mentioned that he should change the class skills and some other little things. But in the end, I'm suggesting the changes without moving away from what the Dungeon Master's Guide says and also, without moving away from what the class is. According to the Character Builder, this is the Invoker:
"You channel your god's power directly. No mere symbol can contain it, for you speak the words of creation, shaping the universe to your and your god's will"
As I was saying, an intuitive divine spell-caster.
There's a guideline for great subjetive questions (which includes this meta-question)
Great subjective questions inspire answers that explain “why” and “how”.
The DMG in 5e inspire those two answers, being implicit in the question, since it is for the D&D 5e system.
Great subjective questions tend to have long, not short, answers
Then again, check my answer in the Invoker's issue
Great subjective questions have a constructive, fair, and impartial tone.
When you manage to give two solutions, being one you like and one you dislike but also solves the problem, I believe the answer more than passed it.
Great subjective questions invite sharing experiences over opinions
I have much experience with D&D 4e and a few with D&D 5e (which comes from quite a few oneshots, but not a campaign). Experient D&D 4e players are well aware of how balance works towards numbers, probabilities, "powers" and other mechanics. We can see how they masked and changed things in 5e, but we can also see what is left there. Using the same logic I'd use in 4e, plus using the 5e DMG guideline, I could create a Invoker that is quite balanced and feels like an intuitive caster (both solutions suggested by me do, in fact, from that matter. Since sorcery points are the main mechanism to make it feel like you can do more than a wizard. Besides, having a number of spells known and not having to prepare any, plus having more cantrips is enough to make someone have the same intuitive feeling. The Wizard based Invoker won't be versitile but balance wise, it is compensated by the other features the wizard provides). About the Avenger, I didn't come up with a decent solution. Or at least not one that convinced myself or my player that likes playing as an Avenger and therefore, that's why I asked the question. PS: I edited this for recently running a oneshot to test the Invoker.
Great subjective questions insist that opinion be backed up with facts and references.
As in, again, the DMG guidelines.
Great subjective questions are more than just mindless social fun.
In fact, those questions might serve as a guide for anyone else who comes asking the same sort of conversion. And if they don't find it good enough, they might add some dept to the issue by creating a new question and explaining why it doesn't work. I see nothing bad about it at all.
