You might find MoonMoon's antics entertaining, but it's pretty much definition of bullying. He's leveraging his celebrity and popularity over people just trying to play the game. This is even more ridiculous considering the fact that he pretty much poop socked only Roadhog early on to the point where people joked he was Roadhog in real life. His style of streaming means that for you sticklers out there he's in a permanent state of 'throwing' because he can't be 100 percent invested in games while memeing and interacting with his chat (not that I personally care but this has been brought up in this thread before that if you don't take certain optimizations or playstyles you are a thrower according to some people). He's in a position now where his stream has reached enough of a critical mass that he can play whatever he want and get tons of views. If you tune into twitch and see some obscure game at the top of the list there's a good chance it's moonmoon or lirik or summ1t or some other variety streamer playing that game. Trying to frame the riddler thing as vigilante justice is asinine because it's clear that he's fallen out of love with the game. He's just doing this for yucks on his stream not some higher purpose.
Probably because he's a strong and flexible DPS that fits a generalist role for the most part. If you're saying that Genji is OP, you're just wrong. He just works well. Balance isn't about whether or not something has a high pickrate. It's about whether or not a character's strengths invalidate too many options or are just way too strong to be ignored. Genji's pickrates are actually pretty stable and not too far outside what you'd expect generalist things to be. He also happens to work well with the things in the game that are actually currently broken, at least in pro games on the previous patch with DM god D.Va.
Generalists by definition invalidate too many options in the kind of game overwatch is. Because every single character is in play all the time, the opportunity cost for picking any one character is the inability to pick every other character in its place. This is huge, and one of the major reasons why Overwatch metas continuously revolve around mirror matches. Generalists filling too many roles block specialists from blossoming in hero drafts. You can quibble on whether this fits the definition of "overpowered" but it's certainly problematic. It's also an issue that will only get worse as more and more heroes are added to the game.
I don't see how anyone could argue that the new mercy is gonna have to less issues with "toxicity" either. A specialized solo rez on a long cooldown? You don't need to be a fancy pants game designer to see that it's a shit storm waiting to happen. Already even after a few games I played and seen on stream I can see the cracks forming on how this works. You have two or more people die in quick succession and have to make a decision on who to bring back. The ones who aren't rezzed get booty bothered. You have to constantly explain yourself every thirty seconds on why you did what you did. You're gonna have situations where mercy's in stacks are gonna be accused (correctly or incorrectly) that they are burning rezzes on their queue partners. You're gonna get more goofy ass elo terrorism i.e. "Rez me exclusively or I throw." You're gonna get more pressure to be on the mic which everyone doesn't want to or can do because there's no interface to tell your team side ability cooldowns like the Z key for your ult. You create another layer of weird complexity in how cooldowns work because you can reset your cooldowns by swapping characters in spawn which makes defense on the second point of Hanamura even more ridiculous.
Old Mercy had some counter intuitiveness because sometimes she had to hide in a spider hole somewhere waiting for the defecation to hit the oscillation, but old rez was at least egalitarian. If you died where everyone else did you got brought back to life regardless of what you or the mercy player felt about each other. Toxicity in games has a direct correlation to how stifled people feel with regards to game mechanics and other players. Specialized solo individual rezzes is greater recipe for problems than a teamfight ability.
As far as "one trick poneying" is concerned, ya'll just have to get over people playing what they want to play. If the game can't incentivize players to play like the game is "suppose" to then it's a failure of game design. It's nothing the community can concern itself with.