The marauder and enforcer are for two totally different purposes. The enforcer is primarily anti-armor, and its splash damage aint that great. The marauder is anti-infantry, and it absolutely demolishes them in the proper hands.
My outfit swipes marauders often, it is great fun to use ;D
And on the issue of chaingun versus jackhammer... again they are two totally different weapons, requiring very different playstyles to use effectively. But the chaingun CAN murder in the proper hands. I have done it, I have seen others do it. I have had terrans screaming their heads off at me because I was merrily murdering them all with their own 'crappy' weapon