I'm a player saying that.
There was always assholes, it's a fact of life. Ignoring them, you have the reasonable logic crowd. That takes the game as at face value.
Vanilla had a superior grouping experience. You ran with randoms and it took awhile, but it was exciting because people react differently to the same things. Sometimes you had people that wasted your time. But well adjusted people move on, they don't dwell on the assholes.
After the game became popular, so did it's dissent. Aspects taken, on the chin, as a part of life, were molded and changed by Blizzard.
Blizzard decided at it's height of popularity that they were going to "by pass" a certain fact of life(grouping and waiting for them), by opening up Randomized Grouping. While this saved time, without a doubt, it removed a sense of community. That sense of knowing someones capabilities and using them for such.
Examples are - Knowing a Hunter/Mage that could kite well and CC. Rogues that knew when to actually DPS or hold off. Or a Warrior that never seemed to drop threat. Or Priest that down ranked. As content revolved around roles that your class was designed for and knowing how to execute them.
Now, all roles are designed around 3 aspects of the game (Healing, DPS, and Tanking) due to Randomization of Groups. This leads to forgotten mechanics and understanding that was once common knowledge. It lead to ROLES in classes being forgotten.
Do you remember Cata launch Heroics after ONE expansion of not doing roles? I do, it was a shit show. Not that I had a hard time, but there were many wipes and the community was at a loss.
If that isn't evidence enough, then I don't know what is honestly. The QoL designs has removed game complexity, in favor of convenience.
So, unless you weren't there.. (when why are you even discussing this then?) then you are being dishonest with the history of this game.