But there are also us who are simply outside the size range any chair is designed for (I've generally been at 90-95kg at 195cm before hurting my back and limiting sports). Unfortunately, but expensive chairs are then usually the only way to go if you want to get a comparable experience to what "average size" humans get with "any chair". I can easily imagine short people having similar problems on the other end of the scale (hurting thighs because their feet can't reach the ground), or simply disproportionate people too.

There is no amount of exercise that will let any human hold a squat position for 8 hours day-in, day-out.

As OP indicates, "universal" design is the problem.