I don’t think this is an issue with MMO games, I think it’s a problem where teamwork is hard. Even just consistently getting a large group together at the same time and not breaking down due to interpersonal conflict is a heavy hurdle. Expecting people to then follow complex plans while also filling the basic roles of the game and not standing in fire is just more than most groups could do.
But it is interesting, and I would say your experience described was not. Large complex team plans are probably not a great model for most games.
I would like to see a situation that required tight coordination among a very small group of 2-3 and light coordination across these groups. Even sweeter if there's only communication between group leaders and intra group.
So it is interesting in it’s own way.
Most co-op gameplay in MMO types of games is really bad. Consisting of either mindless support roles that just cast buffs or heals on a recurring timer without too much consideration of anything else; or of brutally picky metas that require specific movement patterns that you're just screwed on if you don't know them. Especially if there's no communication features.
If you just meet some randoms, don't really talk to them, and just kind of hope they don't kill the run, then forget about them, that's a bad experience. Good multiplayer requires you to interact with other people. Carefully orchestrated raid team crafting is an option without much mass appeal but it is an option. Since it's not really possible to expect coordination among strangers, and there's a high demand for gameplay with strangers, I would say the game needs to be highly reactive. That is to say, your optimal gameplay can't be pre determined. It depends on what they do, and randomness.
The general idea that its ok to just drop into a random group and give it a try implies that the content has to be really easy otherwise people will get frustrated. It depends on the game.