This is pretty much something that I like a lot from Bloodline Champions which also has healing. I don't know if it would be great or not in the game, but in that game, there was a max health that you could heal up to, which was your current health + a percentage of your max health.
For example, Let's look at Scout, Assault, and Brawler with a recovery health pool of 40%
As long as you don't get below 60% health, you can still heal up to max.
However once you get below that,
Scout can only heal up to Current HP + 128
Assault can only heal up to Current HP + 226
Brawler can only heal up to Current HP + 320
Now I can see already that this is very bad for A classes, so of course values could be changed to where they can get a higher % like 45 or something around that and maybe C classes get 35 which would be +144/+226/+280
Just adding more ideas to the mix. Though this would be better for a gamemode with round elimination.
Now another issue with this is that mechs like Sharpshooter can clearly just power shot a light mech to instantly make them go below the 60% or so to where they can't heal up to max again and that would be an awful problem to have, at that point SS would have to change. That's the only mech that really breaks this atm. Just playing around with this as an idea, and looking for further suggestions to tweak the concept to something playable.