Troops vs magic, what am I doing wrong?

[Rookierookie]

Two or three battles will attrition 80 Fir Bolgs to nothing. And typically by year 5 I face armies of 500+, against which thugs work much better.

There are also somethings against which combat thugs don't work well, and tramplers are one of them. The spell Swarm kills life drain thug chasis. Nobody said they are invincible.