TwoSix
Everyone's literal second-favorite poster
I think the point @Pedantic was raising is that any magic capability, no matter how small, will always be superior to NOT having it because having the magic capability doesn't preclude any of the non-magic capability the character would have possessed before.Why?
Now, that doesn't mean character classes are inherently unbalanced simply by the presence or absence of magic. You simply have to set the baseline of what non-magical activities a magic-possessing character to a fairly low level, and then not have the magical ability be overwhelming compared to the elite non-magical baseline a nonmagical class will be able to accomplish.
If a non-classed character has 4 hit points and can only attack with a knife or a club, then the non-magical class that gives him 20 more hit points and 2 attacks with a greatsword will probably be preferable to the magical class that slowly grants him stronger abilities to charm naked mole rats.