Just because you are aware of the team dynamic from your hockey team days does not mean that is the only way to acquire that awareness. Just about everyone has been part of some team at one time or another. They all have somewhat similar "room" dynamics. It is taught in business schools and in Sociology classes. Workplace politics have similar dynamics. Regardless of our experience playing hockey, I think most of us here realize that a team's top players are given a lot of input on things like linemates. It is pretty obvious that they are paid that kind of respect.
A lot of what you are arguing against, railing against, is fans talking about how they wish things were. They know that is just not how it works, but they wish it did work that way. This is a discussion board so they come here to express their ideas knowing full well it is wishful thinking.
Until this year, Scheif and Connor absolutely should have been broken up, whether Scheif was given Ehlers as a linemate or not. Somehow, after all these years, Arniel found a better way. Credit to him. He managed to get them playing a much better 2 way game, eliminating the need to break them up. None of us know how he did it. Maybe it was as simple as telling them that they would be broken up if they didn't get their act together.
I don't recall anyone saying trade Scheifele if he didn't want to play with Ehlers. Some said that he should not have been given that choice. That is not "trade his ass".
And it wasn't just xGF. That is a stat I never pay any attention to whatsoever. It was every stat you can think of.
I appreciate your insights, and those of other posters here who have that kind of experience. But that experience does not give you any kind of authority. Through it you are able to better support your opinions, but your arguments still stand or fall on their merits, not on the fact of your experience.