The wording of the change sounds like it will cause *more* mobs to loose engage status, thus regaining health faster. Your anecdote about stun locking the infinity spawn sounds like there are fewer mobs that loose engage status, so they die faster now. In other words, before the patch the stun locked mobs never had engage status set, and were therefore regaining health faster. And now this patch means that they all have the engage status set during the fight, and are now dying faster. So I'm not sure I see clearly what's going on yet.