I've never had any trouble with any Chomps. I cannot for the life of me understand what all the fuss is about.
Sand Veil makes no difference to the argument, you cannot factor luck into a mathematical formulae, or it would turn into trial and error.
You can't, which is why it's another thing leading him to be overpowered. There is a 12.5% or so chance that your counter (revenge killer really) will not work if your enemy has a Tyranitar or Hippwodon. So that's a 12.5% chance that all of your team preparation was worthless and you will get swept/crippled right away. No other threat has that going for it.
The only competitively viable pokemon with less versatility than Chomp is Wobbuffet. Chomp can only use physical moves, and its item can be discovered VERY easily.
See: Chainchomp. Garchomp can very successfully run mixed sets, and since when has having a mediocre second attack stat made something any less powerful? Is mewtwo OU now because his attack stat is crappy compared to his Sp. atk?
So what if everyone uses it? That says more about the person than the pokemon. Other pokemon can sweep teams too, you know.
Yes, but no other pokemon swept teams like Garchomp. It was on nearly 70% of ALL Standards teams at its peak. You can say so what, but overcentralization is something that is always cited as something that defines an uber. When more teams than not are running a pokemon and all teams are carrying multiple counters, you know there are issues.
There are, in my opinion, ways to determine an Uber. Raw stats (BST 670+, excluding Slaking and Regigigas). Mew is up there because it is so versatile, you never know what it will do next. Celebi, Heatran and the Pseudo-Legendaries have huge weaknesses to common attacking types. Jirachi and Land Forme have pitiful movepools. Deoxys has highly unbalanced stats, so it is up there. Darkrai and Manaphy are both versatile and have moves that concur with their abilities (Dark Void and Bad Dreams, Rest and Hydration). The Lati twins are versatile offensively and defensively and have the Soul Dew to cement their place. Cresselia is overshadowed by psychic brethren that do what it does better. Finally, Wobbufffet is there because it does not function ordinarily, it is more a one-off tool. It is not a sweeper, nor a tank, nor a utility, nor a revenge killer, it is just a blue blob that can take a troublesome pokemon down with it, like Azelf.
Rayquaza has huge weaknesses to common attacking types AND has mediocre speed, it should be OU. Seriously, you can't make arguments like that, most of the ubers have weaknesses to common attacking types. BSTs mean nothing, look at the Regis, Entei, Raikou, hell even Articuno, they're all 600BST and hardly ever used. There are a huge number of factors that decide how strong a pokemon is. Garchomp is an example of a case where the majority of factors are working in his favor.
Even if you do not agree with me, mark my words - Gamefreak is not going to let this uppity little Pseudo-Legendary get away into the tier it does not belong to. Count on it.
This here shows that you know absolutely nothing about how tiers in general function. Smogon's tier system is NOT some binding document that determines how all of the tournaments out there work, in fact most of the official tournaments ignore the majority of our ban lists, and most clauses. Gamefreak has zero control of our tier system, and we have zero control over anything they do, we simply react to what they create in order to create a balanced game. You may choose to abide by Smogon's tiers, or you may choose not to. Nobody is forcing you to do anything here.
Also, there's nothing inherently not-uber about the base 600 dragons/metagross, you can't even use the irrelevant argument that Garchomp doesn't do well in ubers, because he does. Even in ubers the only thing that can really reliably switch in on SDchomp is Lugia. He's not the monster he was in OU but he's no waste of a slot either.