Pokémon X being bad in Ubers is never a reason to keep them in OU. And the fact that he defines the metagame and that it revolves around him is called "overcentralization", another cause to boot something to Ubers.
I think that "uber" just now was meant more to mean "broken for OU" than performance in ubers. Anyway, it is true that "bad in ubers" does not mean not broken.
However, I am definitely of the opinion that genesect is
not broken. At least two posts above reference him "defining the metagame," which "revolves around him". Yes, this would be overcentralization and a great reason for kicking him to ubers, were it the case. However, I truly fail to see how it is--being forced to carry a check to a high-tier (and, admittedly, very high-usage) OU pokemon in order for a team to be viable is NOT over-centralization. Someone very eloquently addressed the IV issue on the previous page, so I won't restate that, but pokemon lowering IVs in order to fare better vs. sect is not overcentralization either.
It seems clear to me that the set being regarded as broken is the RP set--a choice set can be predicted around, while any non-speed boosting set is easily outsped and revenge-killed. A key point in my mind is that RPsect can only have 3 coverage moves--just about any combination can be walled very feasibly. Here are just a few pokes that can easily beat a +1 / +2 LOsect (I'm assuming a moveset from bug buzz, ice beam, flamethrower, thunderbolt, and giga drain--the most common moves iirc) barring one move:
Chans/blissey
Heatran
Gastrodon
Tentacruel
Rain rachi
Any bulky steel in the rain
Dnite / mence
To name a few.
Of these, heatran is defeated by hp ground, gastrodon by giga drain, tentacruel by thunderbolt, and the dragons by ice beam. The pink blobs are hard stops, as is any bulky steel in rain (as someone demonstrated above, rain rachi isn't 3HKOd with max damage thunder--it can body slam, wish + protect, iron head, etc. to take sect down). All of the above pokemon are very much OU-viable, and genesect simply does not have room to run all of the necessary moves to beat them. If genesect were allowed, say, 7 moves and 252 EVs in both attacking stats, he would be utterly broken. But no matter what move combination sect, there will by viable counters to it.
Also, something I think is worth noting: Download is an utterly incredible ability on genesect--without it, I personally believe it would be low OU (or perhaps even below). I just think it is worth keeping in mind that all his "game-breaking" attacks are coming from base 120--which is quite good, but not nearly as much as some of the monsters currently in OU *coughcough kyurem-b coughcough*. In fact, just looking at genesect's base attacking stats, he would seem to make a great mixed sweeper but not a great purely special one. He has no physical movepool however...so in terms of sweeping, he's got to stick with special attacks. Which brings me back to the point: if you can prevent sect from getting a SpA boost, it is really incapable of sweeping. Not a huge point, just thought I'd put it out there.