Wobbuffet is countered by a sleep inducer and Taunt and Trick. Wobbuffet never centralised the metagame in my experience (interestingly) but it did get banned.
Haha, good luck trying to
switch that counter in to stop Wobbuffet! Or does every member of the team carry Taunt+Trick+a sleep move?
We strive for skill in this metagame, not luck. Shaymin-S prevents this. Scizor, Salamence and Gyarados do not rely on luck, Shaymin-S does.
Shaymin doesn't rely on luck to be good; the luck is rather an extra bonus, much like Sand Veil on Garchomp. If Shaymin-S didn't have Serene Grace, I doubt Shaymin would seriously be considered for Ubers.
It has the perfect moves, stats and ability to abuse it. It is really difficult to go around it.
It has great Speed and Special Attack, and decent coverage in Grass, Flying, Ground and the Hidden Power of your choosing. It has some viable support options in Leech Seed, Substitute, and Growth (yeah, it has Swords Dance, but the special sweeper, with controversial moves like Air Slash and Seed Flare, is the set we're most focused on).
However it is rather frail, has a 4x weakness to Ice and 2x weakness to Electric, Fire, and Rock (all of which are among the most used types in OU), loses 25% of its health switching into Stealth Rock, is easily picked off by most priority moves, and actually has solid counters in Blissey, Zapdos, and Regice, two of which are already in the high echelon of OU. Scarf Heatran works just as fine with a careful switch in.
Shaymin-S, with it's luck factor, can have a rookie beat an experienced trainer. It makes the metagame rely less on skill and more on luck.
It can abuse luck far better than Jirachi and Togekiss. That is why it should go to uber. It should be banned for the same reason that OHKO and Evasion moves are banned - to prevent luck.
No one can do anything about luck. It comes and goes. Hell, the entire metagame is centered around luck; the only real skills in competitive battling as it is include making a team, and how efficiently you can execute that team's strategy in battle, through prediction and knowledge of the popular sets. You can't control what team you're going to face (unless you're playing against yourself, haha), which could potentially contain a team that 100% counters your own! By allowing things like critical hits, fluctuating accuracy, flinch (heh), and the chance of not moving due to paralysis, how can the community ban a pokemon that abuses these things to its advantage? How can it ban anything to satisfy this "quota" of reducing luck? How much luck is too much? If the community really was striving to eliminate luck from the game, all of these factors would've been abolished by now. It's like giving a child toys, but forbidding the child to play with them.
Shaymin-S is a different situation. It has many counters. However, since you value the best players so much, some of them think that Shaymin-S is uber simply because of the luck factor.
Just because some of the best players think it's uber doesn't necessarily make it so, as documented throughout history..