The heal tower is the 5th that has a weakness to fire, along with the barricade. That’s way too many weakneses to fire in my opinion.
It would be cool if the heal tower was actually weak to poison, making them the only tower with a weakness to poison instead of resistance. Since it is a healing tower, poison would be it’s natural enemy. And, it would give poison damage some much needed importance on offense.
In addition, there could be an interesting effect like making the heal tower harm it’s allies instead of heal if it’s under the effects of poison.