Totally understand your reasonings but... setting a limit is still a nerf to the roulette though (this contradicts from what you said in Discord "There is no buff or nerf").
Still, thank you for being transparent about this.
I guess we have to wait for another server maintenance/reset to solve it. Meanwhile, maybe switch to view your "Squad" chatbox instead of leaaving the faction?
Mass Healing's HP is based on the affected characters' own HP Recovery. Perhaps those people did not use any buff to increase their characters' HP Recovery first, before pressing Mass Healing skill.