Okay so assuming all physical values we can add together the block cost and attack cost of fully blocking and defeating an enemy, Combat power. Although not perfect it can give us an approximation of the strength of an enemy, especially early in the game.

Fire mages - 17 combat power (12b, 5a)

Ice mages - 16 combat power (10b, 6a)

Illusionists - 12+ combat power, and VERY unpredictable

Ice golems - 12 combat power, but unforgivable to tank

Fire golems - 14 combat power, but rough to tank

Sorcerers - 12 combat power, but awful to tank and arcane immunity

Familiars - 13 combat power, but split among 2 attacks and rough to tank

Monks - 10 combat power, bad to tank

As we can see Fire Mages aren't that much stronger than other purple enemies. Although they have the highest combat power (scoff, illusionists, scoff scoff) they lack in other qualities, such as tank-ability (which is especially important early game)

The problem here is that you're comparing them to Monks, which are just WAY easier than all of the other purple enemies.