Zealot can be the most fun character to play in the game but he can also be the worst player to play if you get into a match with the wrong players. This is not saying that it is the other players fault, it is just a bad matchup.
Sometimes you get new players that hasn’t seen the zealot before and so on, so they will heal you when you are low and you can’t stop them.
Sometimes it is someone with healshare so you spend half the game just trying to run away from your own team.
If you are really unlucky you get a elf with team regeneration or nowdays even worse you can get the healing from the grail knight.
I have a suggestion for how to fix this with a mechanic that is already in the game. Give the zealot a lore friendly skill belonging to warhammer flaggelants. Let us hurt ourselves. The mechanic would be the same as people removing heat from heat based weapons and so on.
Alternative you could adjust that slightly and let us exchange green health for temp health.
This would give us a way to enjoy teaming up with all characters and have some control our ourselves and generally lead to a much more enjoyable experience.
Edit: A fix like this would also make it possible to play Zealot when you have bots in the game, every zealot player knows the pain of a bot suddenly walking up and healing you right when you really don’t need it.