I suspect that the 2.5% Phaser proc is per system so with four systems that brings the actual proc rate to 10%. I don't know if that's true, nor do I know how to test it.
From the number crunching I did (painful number crunching) I determined the proc rate of phasers is at least 8 percent right now. I've heard from better number crunchers than I it's more akin to 10 percent.
I'm anxiously awaiting all the space weapons to be balanced. I don't mind spending points to "specialize" in one type vs another, but they should all cost the same. As it is Phasers and Disruptors are the best primarily because they cost the least to specialize in.
As far as the Phaser proc itself, there are plenty of abilities that repair disabled systems. RMC repairs all disabled systems, so it's nice to have available if your shields or engines should go offline during a fight.
They need it though. No other weapon impacts pvp quite like phasers can.
maybe know but when they all on even field things may be different. At this point in time it be best to leave things the way they are test the new setup once it on either tribble or redshirt then provide feedback.