As an avid player of Sorcerors/Philosophers they have a couple of big weaknesses.
1 As stated above, if the target is not surprised it could take 5 rounds before the Conx5 roll becomes x4 and less. A good warrior could throw a spear or axe in that time and the problem is extinguished.
2 The more peltists/archers on the opposition the harder it is to stay alive
3 Countermagic/Shield - unless you are casting low level sorcery - not really a problem
4 Counter attacks, Nothing like a Disruption Spell to knock concentration or peltists above go for more small damage rather than big damage, keep chipping away at Concentration (Int x 3) with small stones etc.
5 Post spell attacks - My favourite is wait for everyone to burn MP on spells then hit them with Drain Soul - sleepy time
6 They cant move while casting, push the battle lines, Leap, jump, fly, charge - give them a fright and interrupt
7 High Power or High Con always helps
8 Blindness, Darkwall, Lightwall, they cant move and any impediment to targeting screws them
9 Fanaticism, Berserk Shake Earth, Shattering, Fear, Befuddle, Demoralise, Group Laughter, Illusory Substance, Lightning, Madness, Mindblast, Panic
Time is the sorcerors friend, take it away, bypass the minions protecting them use area affect spells if their power is too high, and mutitudes of bee sting type attacks can wreck a sorcerors day