Just an idea I have.. Guess this will take some coding effort from FC, but this is the only way to fix this issue.
Make PvP damage "tag" a player by for instance running a hostile nano in their NCU or something. For the duration of this tag-debuff, any heal nanos cast will do 50% of what they normally do.
The duration of the tag must of course be worked out, but let's say 10-15 seconds or something.
The tag might for instance be applied by adding it as a innate nano formula in all weapons, including the "fists" weapon etc.
To take it even further, let the tag multiply the healed ammount by 0.5, and then also take away say.. half the reflect % on that character.
Never gonna happen of course.