So I admittedly never played WoW. I played Evercrack and City of Heros for a little while way back in the day and based on those two realized that MMOs weren't for me. That being said, I've heard other people talk about the issues with MMOs before and this feels like the worst of all of those.
There's a famous saying that some people like to bring up that "Given a chance, Players will optimize the fun out of a game" and the argument never really gelled with me until I watched the above and realized just how fucking soulless it all feels. I realize people generally want to play the best they can and some people love the idea of mastering a game, but by god, this just feels like they took something that's supposed to be fun and turned it into a fucking job.
Depend what you're interested in, look at all those "job X simulator" game, those are literally job and yet people can play them for hours. And on top of that some people will watch people play hose and even give them money, eurotruck simulator has a decent popularity on twitch iirc.
Raiding in MMO is about three things:
1) The communal experience of a large number of player all coming together, the fun is knowing that everyone is doing their own job to the best of their ability. This fall apart if everyone can just mess around and succeed, the point is the feeling of "we all came together and did something special", the feeling from finally clearing a content you've been stuck on for weeks is something very unique. The best comparison would be when spors team win championship and the crowd goes crazy, except everyone in the crowd was a player. But if a bunch of random people can just pull it off on their first attempt with no special coordination, then that vanish and instead you just get a "huh, that was okay".
2) Content, developer aren't machine, they can't craft content fast enough for player to do if they can all clear it on first attempt. There's some attempt to make randomly generated content (think diablo), but then those all bland together and even though you're doing different stuff every time, it all feel like the same. So you need content to keep player satisfied for the next 6 months while you make the new content, but you've only have maybe 10 hours of content made. So you gotta made it really challenging so that they can't possibly clear on the first attempt.
3) Social experience, most people play mmo to hang out with people and just do something together. But the "something" need to exist so, similar to 2, you need content to keep player in the game so they can hang out with other player and chat. There are some casual guild that are supposedly about just doing the easy version of every encounter, but those tend to die pretty quick, because player will logging the first week, clear the easy version and then will disappear until next patches, the guild become kinda of a ghost town because when player join there's no one there to talk to, so they don't stay meaning that the next person to login will also be alone.
The addon are kinda of double edge sword, because they give such a massive advantages to the player, the dev are forced to make encounter around them existing and make the encounter really challenging, which means player develop better tool/addon, which mean dev have to make those even more complex and this cycle goes on. A lot of MMO will ban addon for that reason, but then as a player you often feel like your fighting against the control rather than the game. Like, I cannot play FF14 because of how garbage the healing UI is now that I've used good one.
That being said, MMO are dying because of how incredibly demanding they are from both the developer and the player, newer MMO tend to be much more casual, but then they replace hard content by gambling content, where you can quickly clear the toughest stuff, but it's almost impossible to get the best loot from them (but if you pay...).