In my opinion, this mechanic is still unique and not boring as you're balancing mechanics of: range ("is this target within range of my lightwell?"), charges ("does my lightwell still have enough charges and do I want to use this charge on this particular target?"), and incoming damage ("Is this target going to be taking so much damage that the hot is going to fall of anyway and be a waste?").
I honestly feel this does not overpower the lightwell or the priest.
I'm curious to see what other opinions are beside my own.