FYI/PSA: If you are asked to leave, you leave--immediately. It doesn't matter if you have a $3000 computer with a fiber internet connection. Most lag these days is a conflict between two players, which is much more likely to be an issue between ISPs, or router configuration, and has nothing to do with your computer or connection speed. Usually people ask the newest player to join a group to leave, and it almost always works for this reason.
If you feel compelled to justify and tell other players that "you don't lag", you actually probably do much more often than you think, since you've been in the situation often enough to get defensive. If you're stubborn about it and other people leave first, it may very well appear, to you, that you were right when the person conflicting with you left, and that just further ingrains this stupid fiction in your own mind. This does not make you right; it makes you the asshole.
It is especially idiotic when you are the only watcher in a game. Who else is going to leave? The players?
Stop ruining games and just leave. Thank you.