> 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.