I agree that wizards have too much ppwer in their mainclass. Thats why I would do wizard as a subclass for a mage like explained here:
D&D General - [+] For (hypothetical) 6e: Which arcane caster class should be the "simple" one?
Well a simple caster does not necessary need to use "spell slots" that concept is complex by its own, but even if onr uses spell slots there are things to do to make it simpler here some ways how it can work.
no spell slots just cantrips but stronger ones or ones which get stronger under certain conditions
Having fixed spells selected (which can be used per encounter or so) instead of having spell slots
Only 1 level of spell slots (Highest level). Tracking 1 ressource is a lot easier than tracking up to 9
You could even just call it spell points and casting 1 spell costs 1 point and they scale automatically like PF2 focus spells
Combined with the above one could also just reduce the number of spell knos A LOT like to 2 or 3.