The easiest way to nerf water heal team:
Ignition cannot be removed by a "remove all debuff" effect if the character is suffering from any OTHER debuff. (so it CAN be removed if it is the only one, also "remove 2" would remove it alongside another.)

I think a large part of the problem with heal team is that it's very difficult to deny the heals. 2-3 global heal+cleanse means that unless you can cc everything, cc doesn't do much. And ignition doesn't deny even half of the heal when they chain them in succession.

I've found water to be much easier to beat on the auto portion of space time. This is due to the fact that you can actually deny a heal. But in live pvp, when they can cast it at anytime, given lags and the effectively 0 wait time before ability cast sometimes, it's very difficult to deny them, mostly based on luck tbh. I rather doubt any kind of reasonable combat mechanic change would alleviate this problem, as Xserver stuff have horrible lag most of the time so it would require unreasonable amount of wait time for every mystery cast in order for ability denial to actually work. So unfortunately, while heal team might be ok "in theory", we can't possibly put the theory to practice and game mechanic makes it supreme.

Food for thought, a player with super high power would choose LM blitz over immortal team if he can beat everyone else with either team.
Why? Because even if immortal is stronger, it doesn't matter as he will win anyway. On the other hand, immortal team is relatively slow where as LM blitz is fast. Why spend one and half minute to win your battle if you can win it in 30 seconds with a blitz?

So at anytime, you probably should not take the top most players into consideration when you want to argue which class/team is strongest, because it's possible that winning/strength is no longer a consideration as it is assured regardless and they are pursuing other objectives.

To be clear, I am NOT saying water is stronger than LM or vice versa. Just wanted to point out this bit.