A fun unit in multiplayer isn't really a good excuse for a gamebreaking behavior in single player.
An examination of what it was that made the Carrier fun might have revealed ways to get similar effects (long range, able to fire while retreating, requires paying minerals for continued use . . .) in a unit that wasn't such a weird gamebreaker. Most people just liked Carriers because it cast a field of enemy unit and Ai stupidity around it. Once players get attached to a unit, you may be stuck keeping it in the game even if it's not really good for overall playability.
Just because it worked with this one unit doesn't mean the overall game experience couldn't have been better with something different in there. But once something is introduced, status quo bias takes hold in a major way.
Edit: I'll concede that you want the AI to be stupid in some ways so that it can be exploited. The Carrier just always seemed to me too extreme.
> A fun unit in multiplayer isn't really a good excuse for a gamebreaking behavior in single player.
Actually, it is. Single player is basically a financial dead end: you play it through X times, interact with very few people, and put the game away.
If you end up breaking it in favor of gameplay where players are generating content on your behalf (each other)... the loss rapidly disappears as people stop playing the single-player because it not only sucks, it's irrelevant.
Then don't use the carrier... Long games against the computer were never fun in starcraft (or most other similar games). It becomes gamebreakingly easy to win if you survive long enough and the AI becomes utterly useless, it is clearly not something that the developers even cared to put some thought into. And that's okay, the real essence of starcraft is multiplayer.
An examination of what it was that made the Carrier fun might have revealed ways to get similar effects (long range, able to fire while retreating, requires paying minerals for continued use . . .) in a unit that wasn't such a weird gamebreaker. Most people just liked Carriers because it cast a field of enemy unit and Ai stupidity around it. Once players get attached to a unit, you may be stuck keeping it in the game even if it's not really good for overall playability.
Just because it worked with this one unit doesn't mean the overall game experience couldn't have been better with something different in there. But once something is introduced, status quo bias takes hold in a major way.
Edit: I'll concede that you want the AI to be stupid in some ways so that it can be exploited. The Carrier just always seemed to me too extreme.