The possibilities are more or less known. The issue is that everything gets turned down. No spells. No flashy superhuman abilities. No blatant supernatural abilities. No stronghold. No followers. No gifts or boons. No guaranteed magic items. No expertise. No movie physics. No comic book physics. No anime physics.
This is where we have to be clear: No design will
ever make everyone and their myriad opinions happy.
The designers have a clear idea of how they want "martials" to act and how they want "casters" to act. Casters have more options to be used to bypass the skill system, but they give up their combat ability. Martials have more combat prowess, reliable until HP 0 at all levels, but uses the skill system just as any other class.
Some disagree because everyone should have the same opportunities but
Wotc aren't filthy commies, uh, I mean...the point is that if you want less options and decisions, choose a martial. If you want more decisions and options, choose a spellcaster. Want something in the middle? Choose the half or third casters.
They've already given us a fighter with the ability to have substantial options both in-and-out of combat and we've placed this arbitrary rule that it can't have spellcasting, even though the only reason we say that is because it doesn't
feel right, yet there's no logical reason why someone would feel such a way. We don't have a problem with magic from a fullcaster's perspective.