Why? The sub-classes of wizards are bad. You lose access to 2 schools for 2 power levels. If it were +10 PL, i would say ok, but +2 is not enough. That needs a complete rework.
+10 PL is way too obscene.
The subclasses aren't really that bad. They are more niche. If all you do is focus in on your specialized school, you are strictly better than a normal wizard in every way possible. Try rolling an evoker, transmute, or illusionist. Conjurers and enchanters need some help because PL scaling is really bad for buffs and summons.
I haven't tried them personally, but I would think that Illusionists suffer more than Conjurers. The vast majority of illusions just get duration and (for the debuffs) tiny ACC boosts from a higher PL. Conjurers at least have some staple spells that benefit from the PL scaling on Damage and Penetration (NecLance, NoxBurst, the Walls, etc.). Are there even Illusions that do direct damage besides Wall of Many Colors?
(That said, the non-spell specialization benefit and excluded schools probably both favor Illusionists.)
Concelhaut's Crushing Doom are illusion spell