[LDiCesare]

Sure : For 10 gems or so, you have a MR 11 thug who dies to 1 thunderstrike. Against 1 mage + chaff, he's going to kill some of the chaff and then get paralysed/soul slain/mind controlled or otherwise magically fried.
The +3 berserk and magic weapon also matters little when you end up trampling most of your opponents, so the strength and attack boost become irrelevant unless you are facing opponents of the same size or bigger.
A fort-turn is better spent buying a dryad most of the time, or a Pan, unless there is no lab or temple in the fort.
Also, a sleeper will be less effective against thugs, but more so against human-sized troops, and comes with a magic weapon for 8 gems, along with having 4 more MR and better leadership, which make him actually suited to fight mages and lead magical troops and shoot arrows from whichever bow you prefer.
Also, lycanthropos amulets eventually turn your units into werewolves, so this build is efficient for a really short period of time and only against a limited set of opponents.
So, yes, what you describe is a very strong thug against size 3 thugs that don't have chaff shields and can't cast MR-negating or AN-damage spells. It is very situational, and I still doubt I would ever want one instead of a mage.