Genesect is NOT BROKEN. A lot of the people against keeping him OU say that his various sets can take out all of his counters with the appropriate coverage move. But Genesect donesn't have all of the appropriate coverage moves! He can only have three, at the most four (and if he has four, chances are he's Banded/Specs, which you should be bale to handle easily if you are a good battler)!
People used argument that Deoxys-S wasn't broken because it couldn't have every coverage move at once, as well. The problem is that it forces you to guess at its set and hope that it doesn't have the coverage move that will allow it to sweep/get past your check.
Not only that but if you don't have Heatran, Blissey, Rotom-H, Rotom-W, Tyranitar, Ninetales, Tentacruel, Kyruem-B, Volcarona, Magnezone (YEAH, HE'S A COUNTER TO SCARF), or RainRachi on your team, chances are you will probably have another Pokémon who can come in on whatever coverage move Genesect uses and KO because 99 speed is just NOT FAST ENOUGH.
Heatran is Genesect's most reliable check, since Genesect has to run uncommon sets with HP water/ground to get past it. As for the rest of them, Geneseect can reliably deal with all of them. Blissey can't take repeated U-turns, Rotom-H is SR weak and if Genesect just u-turns out as you switch in, sucks to be you, Tyranitar gets hit hard by both bug buzz and u-turn, ninetales is SR weak and is 2hko'd by +1 thunderbolt after rocks, Tentacruel can switch in on a flamethrower or ice beam, but loses to it 1v1 otherwise, Kyurem-B is SR weak, Volcarona switching in on Genesect at any given point in the match is very situational since it has to avoid switching in on rocks at all cost, and Magnezone still has to worry about the Expert belt set if it isn't scarfed. I wouldn't have dismissed Genesect's stealth rock weak checks if it didn't have u-turn, allowing it to completely bypass them so easily.
Remember when Thundurus-T came out? Everyone was saying how horrible his speed tier was and how he would't be strong enough because he was too easily outsped? Yeah, he was! And you know who else is easily outsped? Genesect!
Thundurus-T doesn't have access to the godly coverage like Genesect does, making it much less able to sweep, and it also has to worry about ground types switching in on choiced volt-turns, making it less effective at stealing momentum.
Wanna know how to beat Genesect? Hazards. Set up hazards and Genesect will fall easily. The amount of switching that most Genesect do will wear him down quickly. The Scarf set isn't the only one switching in and out a lot either. The Ebelt set also switches because it's bluffing the Scarf.
Oh, really? I would have never guessed. Let's deal with this pokemon that forces switches so easily and racks up hazard + u-turn damage by using hazards.
As for the Rock Polish set, I run a Rock polish Genesect on the team I'm currently putting on display in my RMT (hint hint...click the link), and the Giga Drain set is simply hard-walled by any Fire type. That's all there is to it.
Remind me. How many fire types are in OU?
If it has Tbolt over Giga Drain, then Rotom-W, Gastrodon (and to a lesser extent, Quagsire) all hard-wall it.
Sure, but how often do you actually see RP Genesect not run Giga Drain?
Sun teams also give RP Genesect a hard time. If you see a Genesect on your opponent's team and you're running sun, the way to counter it is to GET YOUR GODDAMN VENUSAUR OUT BEFORE THEY USE THEIR RP GENESECT. I use one! I know! You get Venusaur out before Genesect, there's nothing he can do about it.
This is true, as long as you have sun up.
And what about Breloom! Adamant Fight Gem Mach Punch does a hefty amount to Genesect, so if you have hazards up and Breloom, Genesect is going down. Or, if you get a swords dance up before Genesect comes in, then you can straight up KO it right there with the Life Orb set. Even if you don't if the Genesect is using the LO set, then just let it whittle it's health down before you send in Breloom, and THEN KO it.
Genesect is very rarely going to try to deal with breloom, and, if it does, it's going to be in in great health, since your opponent will know that Breloom is going to deal ~55% from a +0 LO mach punch. Saying "whittle its health down before... breloom" sounds great on paper, but, as I just said, Genesect isn't even going to attempt to deal with it if it isn't in good health.
The point is, if your team doesn't have any of those things in it, I'm sorry, but you're just not prepared for most of OU! If Genesect is the most common threat out there, why don't you have one of those things on your team? That's a pretty long list of things you can add to your team, one of which is just "fire type!" That's a pretty simple thing, isn't it? I just think that Genesect is way easier to counter than people are making it seem.
You're oversimplifying how easy it is to deal with. While it's true that most of the pokemon you listed are able to deal with some variant of it, Genesect has a way to get around all of them by itself, bar heatran (Even though it can use HP ground/water). Lastly, using bolded, all caps phrases doesn't make your point any more convincing.