I can keep Predation up 80% of the time in combat. Just stay close to the ball carrier and keep fighting, and don't carry the ball.
Alacrity is not in the same stat pool as power. It shares a stat pool with accuracy and surge.
I bet you a million credits that Alacrity can't stack beyond 7% with diminished returns in PvP gear. Think about it. If DPS increase given by alacrity is much higher than the other 2 secondary stats, surge and accuracy, will there even be a point to get accuracy and surge anymore? No. The most logical outcome is that alacrity, accuracy, and surge are balanced to give similar DPS boost, so players can customize their play style by choosing which stats to invest in. If alacrity does give too good of a DPS boost in the beginning, I can bet on it getting nerf to balance out with accuracy and surge, because that is the design goal.