i don't get what about the premise of rage or focus themselves actually requires them to be any sort of supernatural effect, sure there might be subclasses which come with supernatural effects but the abilities themselves not so much, battle frenzy is a thing, self discipline is a thing, they don't need the supernatural juice to make them work,
and i agree fighters and rogues shouldn't have to wait until level 10 to do cool things, what i object to is them needing to be some sort of chosen one or demi-god or super soldier to do those things, PCs can be special, and what's special about a fighter can be the amount of training they dedicated themselves to and having the willpower to push past where most lesser folk would've simply given up.
there are plenty of people out there who want to play entirely non-supernatural characters who still go toe-to-toe with gods and abominations, making every character who wants to play at high level dependent on magic to be capable is denying a swathe of people who want to play one of the most classic stories out there, i deny that the 'supernatural event horizon' as micah calls it, has to exist.