The dumbing down and homogenization will mostly come down to players not knowing how to work together with the strengths a class AND a player brings, because more likely than not, players won’t know and will refuse to learn what other people are doing. They follow the guides, think they’re doing things perfectly, and blame others.

Massive runoff sentence here, but no, this is incorrect. It's been stated by the dev team on multiple occasions (in the WOTLK-MOP era) that the intent was to move away from raids having strict compositions and feeling required to bring specific classes over friends. This is something that has been taken care of by the introduction of crafted profession items that fill those gaps if needed.

Talk about overcomplicating a simple discussion.