So all you have is indeed "muh feels"? Because all the things you're listing would happen anyways, it just would take time. On Icecrown especially it would already have happened even if people didn't get a single item out of their donations. The fact you keep having to point out "months" just shows the real issue is your personal sense of accomplishment is based on "I have, they don't." You having it doesn't matters, because someone else got it in another way or faster than you. How do you deal with the fact that something you might have tried for months to get could drop to someone else on their very first try? Are you going to rage about how that's unfair, about how you put oh so much effort and they got it so easily too?
But it does affects the game play, as Jim would explain to you. It might not be a mechanical advantage, but it still affects it. Simply playing the game isn't enough for most of the players, they also want to look good. It's the very reason so many people freak out over transmogrification. People feel accomplished if they wear a skin they like or if they can spam that annoying emote over and over. It can be more important to lose looking good than to win with a default skin.
And he's correct. But you, with your "it's just cosmetic," can't see it and are part of the problem.