Power launchers don't really suck. They have their purpose, and that's particularly being able to take on average 20 more points of damage than Power Blows.
Some characters already have powerful-enough juggles that they don't really need them though, like Hitomi.
They just seem to take too much risk. The timing to land one after a critical burst is much stricter than a power blow. Then once you land it you have to perfectly time when your opponent descends back down from Mars to begin your combo, assuming you don't drop it. This isn't even taking into account online lag. I'll just stick to the power blow for guaranteed damage and work on my fundamentals more.