No decent guardian will have focus generation issue's in Shii-cho, hell I don't have much of an issue in Sorensu either. I think the heal should tick on its own and heal 8% of health every second for 5 seconds. Maybe a 1 min 30 second cooldown on top of that. Otherwise, it really is useless in PVP.
This really isn't OP when you consider the viability of shadow/assassin tanks in PVP, or even sentinels/marauders. I usually die 3-4X more on my guardian than on my assassin or sentinel. I do far more damage on my assassin and slightly more on my sentinel. The trick is, their defensive abilities (with low cooldowns) make it very easy to survive. A guardian on the other hand, has no escape and less mitigation in shi-choo. So while we always still take dmg, the other classes can escape and take none.