Wish is one of those things that just takes a lot of experience and system mastery to handle well.
Like a barbarian wishing for faster or more precise weapon attacks? Sure whatever. Damage is the easiest thing to account for and barbs are in no position to risk taking it too far. (I'd probably do something like letting them turn one miss a round into a hit instead of just adding attacks. That is both more logical as a narrative wish request and doesn't just shift stuff up for no reason.)
Getting extra 9th lv slots on the other hand is risky as it allows power banking to occur with less effort. Safer to give a free cast of a list of spells or automatic max up casting of a certain spell. A meteor swarm is big but nothing compared to binding summons over and over.