Reduce MAX HP seems to have a hard 70% limit instead of reducing for set number of turns

I have equipped three champs with DESTROY only to hit the 70% limit so i equipped all five and the exact same 70% limit occurs only faster

--- resulting in wasting TENS OF MILLIONS OF COINS trying to  get max HP down just just a little lower to kill last bit.

ALSO

the each turn 50% heal is more like 80% heal of max hp

resulting together i have gotten close to a sliver of killing it only for the heal to take it up to almost the entire way back up

if either bug were to be fixed I could easily kill but I've gone over an hour with endless loop of getting close only to have it heal up to almost max.

using PC exclusively (so i cannot check if a phone app acts different but i assume so or everyone would be complaining