Then I would not have understood it, and would instead have interpreted your message as saying to me, "Homebrew need not have any rules nor consistency whatsoever, it is and can be
truly anything, without any limits. It is inappropriate of you to expect limits of any kind, least of all consistency."
Sure, but in this thread we were also talking about torching the very concepts around which PCs are built. (I was certainly making that strong implication.)
With that as the use case, every assumption of normal PC progression is open to being analyzed.
I would deeply and fundamentally disagree with that notion. That's like saying that, because we're re-doing calculus, we not only can but
must go back and break every single axiom of
arithmetic too. It doesn't follow.
"We are completely rebuilding the classes
that actually exist" is not the same as "We are completely rebuilding
the entire mechanical space in which classes exist". The latter does, yes, mean that we should question why (say) Sorcerers get this spell but not that spell, for example. But it doesn't mean that we should completely obliterate all game structures and start from a blank mechanical void.
If one class can now cast 4th level spells at character level 4, that embarks us on a complete rebuild, not just of class mechanics, but of the entire spell list, which is easily a quarter of all of 5e's rules. (It still fills me with...I guess "poetic shadenfreude", since it's not regular schadenfreude but like it, given that 5e has very nearly made all characters spellcasters, given that was literally one of the complaints that went into inspiring its creation!) Your proposal read, to me, like saying, "Let's
simplify the classes that exist, so they can be presented in this way", and not even
slightly like "We should scrap the ENTIRE 5e system, and build a 6e that produces characters like this."