Like yeah mercy mains get mad when she gets nerfed, but the most vocal by far are dive characters. Go to any sub for doom, genji, tracer, ball etc and they’re constantly complaining when they lose or get nerfed or get countered. Obviously no one likes when their character is nerfed, but I see complaints about it much more from doomfist players than from people who play say, ashe or torb or something
Because dive characters are designed to rush headlong into the enemy team, and doing so requires a combination of good situational awareness and their own team being ready to back them up. If one or both of those requirements aren’t filled, the dive character will get focused down and shredded like paper.