Prator: Fully upgraded heroes - especially psykers - attached to a squad can do incredible ammounts of damage. That thing that destroyed your dreadnaught in 2 seconds WAS a hero, after all :D
Also: People, it's not me being so good, it's you never actually playing the MOD!
Fenixp: Well, yeah, but you had a fully upgraded Mek WARBOSS, a hero only available when you're at tech level 3 and in possession of a relic. Of course it's going to be the strongest thing on the field when it's souped up. If, on the other hand, you just throw a Space Marine Captain out onto the field with no boosters, he ain't gonna last.