Geo is not lacking cc. Fossil Strike and Impalement are awesome as they don't even require you to rid the enemy of magic armor. Also, they will even slow them down if you cast them in combination with fire traps -- which they technically shouldn't do, as all the oil is supposed to explode instantly, right? Worm Tremor prevents characters from moving or teleporting for 2 turns and Earthquake knocks down enemies in a very large radius. IMO geo is the most versatile school for cc
Also, both of the latter only affect enemies, which is extra useful.
Fire sucks at cc, that's for sure, except for Fire Whip which has a very limited range. A very situational spell sadly.
Air damage is problematic, as it is pretty easy to stun your own party members if they stand in the same puddle of water or blood. Also, there is no reliable way to make elemental affinity work with Aero.
If you like using summons though, you might want to consider Cursed Electric Infusion. If your summons are the only ones in melee range, this is probably the easiest way to stun groups of enemies without hurting your party members. Your incarnate would then get Closed Circuit and Electric Discharge for free.
