Welcome to the FPS, where one weapon is better than another.
Seriously, learn to play the game. If you're consistently having trouble with such a limited weapon you need to re examine your tactics. That grenade launcher is neither particularly powerful or even the worst grenade launcher in a game! (or the record the superdragon in Perfect Dark wins that one) But you know why people complain about the MW2 one? It's because games affect your rank. Stop caring so much about a game and just learn to cope with it, MW2's guns are some of the more restrained ones in FPS history so you've just got to learn to beat it.