In my opinion, that 0.2 of a second alacrity takes off both of your biggest heals is a life saver in pvp. Both of your own, and others.
You're not getting 0.2 off one cast in the scenario I outlined. If you have the 4% talent and 100 alacrity, KI is at ~1.85s. Adding even 200 more Alac will only shave off 0.11s, not 0.2s.