I have a feeling that the higher the level, the less being able to purify is the relevant factor, but the time it takes to actually purify is: noticing the crowd control, there is a minimum human reaction time there, the time for the action to be sent to the server and back, and the time for the action to actually take effect and the animation delay to go through. Generally this can be enough to just make you lose enough time to fall behind on healing yourself and this ends up with you dying.

Still an early reaction though, I have no idea how I'll feel about it in months.