Why am I so bad with Dom3

[Endoperez]

I'm not good with thugs, myself, but it depends. If you're facing huge armies of chaff, several commanders equipped with Charcoal Shields even the odds greatly. If you're facing armies of Soul Slaying mages, several high-hp commanders with outstanding magic resistance (through Starshine Skullcap, Amulet of Antimagic and/or Lead Shield) will protect your other units.

Couple of strong thugs equipped with cheap items (for luck and ability to kill several troops/turn without getting too much fatigue) rampaging through your enemies' weakly defended provinces can be quite annoying as well, especially if they can fly, sail, are stealthy or otherwise able to move in ways your enemy can't easily anticipate.