Well for starters the problem lies not with the elf since GK also gives green hp, and the GK version heals to max as well. There also exists healshare and just plain medkits.
There’s a very simple fix to this which is to give zealot a passive which either blocks healing from allies or converts it to temp. There’s just no reason that allies should be able to ruin zealots entire reason for existing by running certain talents or RNG. Quick fix this and then look into more ambitious stuff like reworks.