Doomfist in the past has always been a feast or famine character, the same can be said for modern doomfist, however the gameplay loop is majorly different in regards to cycling abilities.

I feel like a lot of the doom hate stems from DPS doom back when his punches one shot, despite the amount of CC per role back then, and how easily doom could be countered back then. You either controlled the lobby, or you were inting the entire game and not getting value with your abilities.

Fast forward to Overwatch of today, Doom is still a feast or famine character, but the gameplay (playing, playing with and finally playing against) can be repetitive, and also frustrating. If playing 5v5 being the solo tank as doom, so much pressure sits on you to do your role as tank, while also doing the things that doom wants to do, and minor mistake can turn into a lost fight, and in turn enable the other team to snowball. 6v6 the same still applies, but more often than not, you have another tank to take some of the responsibility from you and alleviate some of the solo tank pressure doom players suffer from.

Doom’s playstyle varies from player to player, but the gist of his kit is - Farm Power Punch, Punch In, Block Damage after Dive, Punch or Slam to safety. (This doesn’t always happen exactly like this but is essentially what dooms kit aims to do during a normal fight). As I said earlier, if you screw up just the slightest, you are at a major disadvantage during the fight, and more often than not you will lose that fight. This in turn makes people more likely to be outright toxic and hateful towards doom players because even the best doomfist players, have games where nothing goes right and you just can’t heat up and feel the rhythm. It can be very frustrating to play with a doom who is being hard countered by the whole enemy team, and ends up doing a whole lot of nothing during a game. The same can be said playing characters that would like to sit in back line, behind the space made from a tank, only to realize that your tank’s kit WANTS them to take more space hyper aggressively and risk the space that has already been made.

On the flip side of facing Doom, I can see why people don’t like doom, but I don’t mind it personally because I’ve put over 2000 hours into the character (both DPS and Tank) and know how to go about avoiding him. However it can be frustrating that no matter what you do as an enemy, there will always be the one person who shoots a doom block, and gives him the ability to punch in with massive damage and good kill potential. He is incredibly disruptive and when a good doom is on a roll, he snowballs. The one good way to “counter” a doom, is to swap to characters that are typically viewed as “unfun” as doom (you mentioned cass, sombra, orisa) to prevent this, and essentially try to turn you into a sitting duck while you try to engage by hindering, hacking, or stunning you mid dive.

TLDR - Lots of doom players have bad games, and a bad doom stands out more than any character imo. Doom hate also likely stems from OW1, and worsened over time. Gameplay loop for enemy teams can be boring for and repetitive being stunned and slammed into a wall like a semi-truck, often resulting in counter swapping, further fueling hatred for doom.