It's not an ideal answer, in my opinion
Rather than citing any 5e design guidelines (e.g. the DMG's guidance on "Creating a Spell") in explaining why the sleep spell doesn't work the way OP thinks, your answer simply asserts that if it did work the way OP thinks, it would be something like the homebrew spell you made up as an example. It doesn't cite any relevant rules; it simply asserts that certain things are true (though you do briefly explain your chain of logic).
Essentially, you explain your own design philosophy in creating a different sort of sleep spell, but nothing in your answer provides evidence that this is why the current sleep spell doesn't work that way.
Moreover, your own answer basically states that this is a homebrew suggestion as a solution to OP's problem (i.e. a sort of frame challenge: "It doesn't work that way, but here's how it could"):
However, this is a cool idea and this is what you would need to do if you wanted it to work that way.
(...Even though the sentence immediately afterwards claims it's not a suggestion. You're basically saying, "Here's how you could make it work. But wait, I'm not suggesting you make it work this way." It's sort of self-contradictory and unclear.)
And if you're suggesting homebrew as a solution to the problem, then it does need to be supported by evidence and/or experience, per the "Good Subjective" guidelines, not simply by "spitballing".
In short, actually designing a homebrew spell is unnecessary to answering the question; it would be sufficient to simply point out any flaws with the OP's misconception of the sleep spell, and cite the 5e design principles/rules violated by their misunderstood version of the spell.
A related discussion on meta: How should I provide examples of experience as support for my answer?