I think that one big issue is that, of your 3 bullet points, the one that happens the most often is the 2nd one, but that's also the one that's weakest in a multiplayer game.

Stifling a fetch land is a huge tempo swing for one player--potentially crippling their development, depending on how much they were relying on the mana and color fixing. I've had tons of keeps on hands that would have been completely blown out by a fetch Stifle.

But while it massively hurts one player, it also puts you down a card and a mana while two other players are perfectly fine. It's like Bolting a Bird or a tempo counterspell. Could be a game-changing play in 1v1, but it sets you back relative to the other two players that didn't expend anything. That's fine if what you're countering would otherwise swing the game for you (like your 1st and 3rd bullet points), but it's less fine as a 1-player tempo setback.

So really, I think the major pros of Stifle that should be considered for multiplayer EDH are just your first and third bullet points, at which point I think it isn't surprising that it feels a little lackluster a lot of the time.