What level should this exhaustion-causing spell be? was asked and includes an element of homebrew, but has only 11 specific answers it can possibly be.
The question presents a given spell, and asks which level it should be. The possible answers here, given the 5e system, are: cantrip, 1st level through 9th level, and no level (ie, the spell is unacceptable).
On further checking, justifications that answer givers have provided have a fair bit of opinion, but seem to all be based on sound reasoning and experience. There was even a frame challenge to update the spell and make it better.
To contrast, I have asked two questions along the same lines before, and neither were closed. One was of a homebrew metamagic asking for how many Sorcery points it should cost, of which there would only be a specific numerical answer; and the other of a homebrew magic item asking for the appropriate rarity rating, of which there can only be five answers (Common through Legendary).
Though the question about spell level is about homebrew, it seems that it can be answered based on comparing the effects of this to pre-existing spells and conditions. For instance, the given spell was clearly better than a cantrip or a 1st level spell. There are guiding principles at play that experts can draw on.
I suppose, bringing up the existence of the homebrew tag also justifies this a bit.
Should the question have been closed, and why? And the more general question here is, should all questions of "[How Many/What Level/etc] of X should this Homebrew thing have" be closed as well?