I haven't played OU in a month or two now, but when I last did my ranking was around 1100 solidly. I just want to give my opinion here for bans to better the metagame.
Excadrill: Yes, people have said all of the arguments already for me. Excadrill needs no set up, only sand to be out, and you can't run scarfers safely. Anything fast yet frail has a poor chance with Excadrill outspeeding it to succeed. Being almost forced to run a pokemon to deal with excadrill is bullshit, and I sure as hell refuse to run a gliscor, because my team synergy is completely bullshit with a gliscor in it. If you want to run a team of your own with its own unique synergy, you often will find that you can't, because Excadrill is such a force that you need to have something to stop it. The speed tiers are messed up as well, scarfers are not common from what I've seen, besides something like Rotom.
Thundurus: I originally thought that he wasn't broken, and quite managable. But between prankster twaving half your team (good luck if you were relying on sweeping!), and being able to run a different move to switch between which of his checks he wants to not have as checks, thundurus is not an easy pokemon to stop. His speed wouldnt be an issue if scarfers could play safely, but with Excadrill in the game, scarfers probably won't chance it. Taking a thunder in rain is not anything someone wants, and thundurus can just enough survive hits from full health (took a modest 252 shadow ball from my chandelure and lived one time). If rain and excadrill were to be banned, then I would very much drop my suspect on Thundurus's brokenness in OU.
Auto Weather Abilities: I'd waste my time writing a few paragraphs on my thoughts about how much shit this metagame has turned into because of weather, but there are plenty already in this thread, and despite my hope, I'm very sure weather won't get banned, because it is simply too easy for people to copypaste for easy wins. Weather teams against non weather teams have a significant advantage, and unless you run your own weather (adding to the stirring pot), or are forced to run crap like hail on a random pokemon, the opponents team is set up from the start. People are even saying ridiculous things like "this is the weather meta", and usage stats show that it's so centralizing. Gastrodon, an effing RU, is now in OU, because he happens to be a good counter to rain. Celebi, formerly UU, is now in the top 20 because she is a good counter to rain as well. Tyranitar usage vs Excadrill usage has even shown that Ttar is now being used as an antiweather pokemon instead of just another goddamn sandstorm team. It is restricting. Half of the people in the tier have a weather team, and if I were to guess, I would say up to 75% of all teams have something to do with weather, be it copypasting a mindless strategy or being forced to counter weather. I have seen arguments saying that weather adds variety to the game with it's own teams and archetypes, but this is the most idiotic crap I have heard from any pro weather arguments. Yes, you are true in that it adds more viable strategies, but that doesnt matter worth a damn when it becomes the only viable strategy. I have never seen as much lack of variety than from weather, because no, it is not just another team type like trick room or gravity (those add REAL variety), it is a centralized overpowered force that everyone is starting to run because they realize they have no chance against it or they want an easy win. The bans from past rounds have seemed like holding back. Extremely holding back. Ban manaphy, ban swsw+drizzle, what's next, a ban on thundurus only? This is only showing weakness and unability to put a stop to the real problem. People keep cutting the heads off of the figurative hydra, but that will never kill it. Take away an abuser, stop the strongest ability in it's respective weather (whats next, chlorophyll + drought? ha), but the body of the hydra is still there. Every one of these nerf bans has had weather in common as the central power unit. Just ban the thing at the center, the real problem. Weather needs to gtfo.
On Garchomp: I would definately try to adapt to him if weather was banned and he was brought back (actual chance of both happening; almost nothing), but I'd VERY much prefer that he stays in uber. Garchomp was banned last gen, what changed for him this gen? I don't think that you would want to fight a garchomp at +2 in rain, or at +2 in sun, would you? Random hax was only the icing on his broken cake. He has good speed, amazing coverage and typing, and hits effing hard. Not to mention he has bulk as good as swampert. Yache berry DD or Scarf versions are both deadly. Garchomp is fucking broken even out of sand. Before Chomp was banned this gen, I fought him many times, and there was no difference in his power in or out of sand. I could miss maybe, but he still was at +2 and had amazing coverage and stats. I got sick of him a few days before his ban and was just about to use him on my (non sand) team just because I had fought him and knew that he was overpowered, and I wanted to use him just to get some easy wins. Garchomp needs to stay where he. is.