1) They can only be used once per round (and when you're at 50% health, no less).
2) They require a certain charge time to execute, so it ain't a fast move to just throw out against a player who is on-point.
3) Power Launchers don't even guard break on block, so you can get throw punished against a player who is on-point. At the same token, Power Blows don't even guard break until you're at 50% health.
4) Power Launchers compensate for some characters who don't even have a ceiling move.
5) Power Blows compensate for those who want to play it safe after a Critical Burst. Sure, PL combos may potentially deal more damage, but sometimes it sucks when you drop that combo. Also, special dangerzones.
6) Both are highly recommended to be used after a successful Critical Burst (when you're at 50% health).
Now, if you wanna talk stupid, try Power Blows and Power Launchers done an unlimited mount of times per round no matter how much health you got like in the pre-alpha build with guard breaks intact. You think you know stupid? In these conditions, you'll long for something as sweet as stupid.