Currently counters and maxhp reduction are both balanced around their interaction, changing the way they interact would necessitate a look at the power of both counterskill units and maxhp hate on a case by case basis case.
Your current argument simply revolves around you wishing the mechanics of the game to be different because you feel that they should be, i could as well argue that counters should be checked at each stage of a grimoire or that closing should resolve after each grimoire/openskill, i dont though because i understand the rules of the game. What happens if your heal grimoire resolves after a fire arrow? should that have happened? if you think that counters happen when you get hurt then perhaps it should but once you understand the way counters actually work then it makes sense. Does it make sense that you can activate your own counters? to a lot of people who start the game its a surprise, certainly by definition it makes no sense at all.
Yumenero made the point that maxhp is more important than other stats because it removes the cards presence, i would counter with the fact that by reducing other stats you can reduce their usefulness, a card that has been made useless is often worse than a card that is dead.
You make it apparent that your reason for wanting to change the rules is because you think that counters are weak enough without maxhp hate not triggering them, this can be seen most clearly in your statement that 'counters already have a weakness'. Which brings us full circle to that magical word, balance. Guardian was once stupidly strong, thankfully we were given a way to help deal with it enter warning knife. Before the advent of plentiful removal and stat powercreep maxhp was the answer to counterskills, its existence provided justification to the existence of guardian. The problem is that things have moved on, now stuff like serpent and bringer just rawpower through a guardian so maxhp feels surplus rather than a neccesity, this probably shouldnt have happened but the problem is not counters or maxhp hate its the stats of the counterskill units in comparison to the damage readily available in folart.
Tldr: maxhp is supposed to be the counter to counterskills, powercreep in the damage department has outpaced the powercreep in the survivablity of the the counterskill wielding units.

