Wizards are both too weak and too powerful at the same time which is hard to pull off.
By overpowered I'm talking about how many spell casts they will have per encounter. At level nine they have nine casts, at the same progression they'll have eighteen casts per encounter. So many that they'll never run out and can start every fight from stealth with their best nuke or CC, then bang out a few instant cast buffs and then work their way down from the top of their spell inventory.
The spell power gained doesn't seem to make much difference, the penetration gained is less than one so it doesn't help much.
The build I'm looking at is an Arcane Knight - Mage/Paladin probably Bleak Walker. Paladin defenses plus Wizard buffs plus summoned weapons when desired plus getting all the spells for free from found Grimoires looks to be solid. At max level i think they get to level seven for spells so that'll be 13 or 14 casts per encounter for a guy who'll be whacking things in melee generally.