I think a lot of people assumed originally that casual mode would just be the same as ranked mode, minus the ranks and leaving penalties (like boot camp and MvM) and pubs would remain their own thing.
Honestly, I thought pubs would be their own thing too. To some extent, they still are, but the complaints about lack of vanilla servers are frustrating simply because people are too used to Quickplay rather than Server Browser.
Also leaving penalties are ass. They are standard in most multiplayer games that are ranked but I’m glad Valve did something about them. It’s one of those things that very, very theoretically sound decisions that end up being very, very messy in execution. OW is still struggling with leaving penalties to this day, albeit I don’t think it’s as bad.
(Also that Avoid Player shit in OW a while back was dropped because everybody used it to their salt’s extent - see: best Widowmaker player not being able to find a lobby since everybody used it to avoid them.)