To achieve those two ranks in every school, that was 15 ability points, or slightly less than 25% of the total ability points you can hope to achieve in the entire game. You are not going to be able to max out all five schools of magic. You can learn higher level spells, but they will come with AP penalties the greater the difference between your ability rank and the rank you need to use them without penalty.
So yes, you can learn a bunch of relatively low-level spells, but higher-level ones will require you to save up much more AP than it would if you specialized in them, and saving AP will drop your damage output per turn, and your warrior will be able to fight each turn.
That's the theory, anyway. It's quite true that we have not tested out high-level play in the beta, and you may indeed be proven right.
