Another thing I hadn't quite considered until playing with those changes is that if you get focused before using your DNC LB (as again, players at a certain level with 2 braincells will do), odds are you're going to eat damage as usual, but also crowd control, which can force you to heal and Purify before using the LB, which means that Purify won't be ready for after the LB unless you delay even further.
Or you can just retreat and try again another time when nobody in the enemy team has hard counters to your LB, when you get positioning, and when basically stars align.