Honestly, I think you can add health to all categories, unless you're already 100% Ult6.
I had health problems, all the healing features were saved, I recovered my health, etc. Etc.
In addition there are synergistic properties, effective anti-blockers, high armor have more, those that get buff and regenerate preserve and care more, on the only negative bleeds more, but only for a small percentage of% that you added, so it's not so bad. DD will be beastmode.
The Tech already have a high armor, a bit of good health (hi CB), some extra protection there (hi Vision) = more value from any other health. The mystics there are healers and some dodges and some reanimation and healing here = more value from any other health. Health is IMO without a brain.
Too much to spend? I would completely ignore the Mutant until we have a team in the early evening. We do not have yet a 5th yet. But at the end of the day, focus on the best teams, 10/12/15 characters that you use, look at what it looks like. Take a look at the one with 6/7 stars, you can star (for example BW, Vision difficult to do). See your categories.
So far I think I've made a mistake, but we're still controlled by the alliance level – I've entered a point in Armor by skill. Which is not lost, I'm always raising Mercs and some Minion Shield for example. I'll probably slow it down until those guys start again. Being interesting to see if and how FN allows us to restore things, I'm sure it will have a good penalty / cost if they do.
[At least one free reset / way to gain such resets over time would be nice]