The Warlock’s attack can be 15-20 points higher than the Wizard’s (which is practically double the damage) – that’s two.
In addition, the Wizard spends 1 turn on a counter-spell (because it’s a skill), while the Warlock spends 0.7 turns on spells (because of spell mastery) – and that’s three.
Therefore, I think it’s not always advantageous for the Wizard to engage in such an exchange.
As for the Dwarves, the Warlock’s CHAOS potential is so great that a large amount of HP and magic resistance may not help. Although, it’s true that summoning is a better strategy against Dwarves.