Zygarde :)
If I were you, I'd keep the sarcastic comments to a minimum, and when you use it, try for a positive connotation.
Anyway, since I assume I'm one of the other players you're referring to, I'd like to clarify. X is more dangerous on more teams, because its easier to use. You go in, boost when possible, and blow shit up. In that regard, its arguably the best there is (if you read my signature, you'll understand why I say arguably). I personally use it as an early game sweeper to give me a lot of momentum and it often will KO 3-4 pokemon by itself. If you're looking for a pokemon that will immediately cover a team's weakness and give you a lot of offensive presence, I'd say X is your guy.
While X is usually put in late in a team's planning (It can be part of an offensive core, but I've tried to plan a team around X, and it wasn't that easy. I ended up with 2 checks for Heatran and 2 for Azumarill, and only 1 support pokemon. You can imagine how well it did putting all the weight on X's shoulders), teams usually need to be built around Y in order for it do its best. He needs a lot of support for things like stealth rock, but he also gives lots of support with Drought and eliminating tough walls. After I use him to blow up whatever wall my opponent had, I usually save him for the end as his decent speed and incredible offensive power make him a great late game sweeper.
I personally have 4 OU teams, and right now the one with Y on it is ranked higher than the one with X on it because the Y team better suits my personal playing style. I told you X earlier because Y is harder to fit on a team, not because one is better.
When building a soccer team, you don't get all the best players you can and put them on a field, then you could end up with a million forwards and nobody to defend. You get the best defenders you can, the best forwards you can, and so on. In my opinion, X is the Messi of pokemon. He can charge forward and get points on the board. But not all teams need that star forward. Y is more like a midfielder, who will protect your team from dangerous pokemon that could cause your team problems, but he can also play an offensive presence to KO a couple of pokes itself. You can make arguments that one is more important, but since they do totally different things, there's really no point to it
P.S. Sorry to all the not soccer fans, I'm writing this while waiting for my friends to pick me up for a game, so its on my mind