Ugh. The more I think about it, the more genesect deserves to be uber. There is literally no pokemon in the game that can come in, take any move, AND KO. Oh, chansey? Take >70% from my CB U-turn. Jellicent? Get 2HKOed by my boosted thunderbolt. Heatran? Let me just U-turn out to dugtrio, and then unless you're running shed shell (why in this metagame are we using SHED SHELL HEATRAN), then GG genesect sweep.
Genesect is more manageable in practice than you said here.Each set can be dealt with the right moves and pokes.Firstly,Scarf Genesect has to lock itself in one attack when it's not using U-Turn.So you can simply use that and gain momentum on your side.CB Sect can really surprise you and might net a kill,but once you know it's CB,it can easily be dealt by exploiting that medicore 99 Base Speed.Rock Poilish set,from using it is certainly one of the most dangerous and underrated sweepers in OU,however it still needs to get rid of special walls to sweep.Furthermore,you can actually "predict" it.If you see the opponent not using Genesect to U-Turn about or attempting revenge kills,and instead saving it for late game,you can guess that it's a RP set.Also,the RP set has similar move pools for Scarf and Ebelt sets so,If you bring something for them,you can deal with RP genesect.
Genesect is not Uber material imo.It's perfectly fine in OU.I never had any game breaking problems facing Genesect.Sure,it's really good,hard to counter and has a lot of options but still,there ARE ways you can deal with it or check it.There are plenty of mons in OU that cannot be Hard Countered such as Terrakion,Salamence etc.But there are methods to beat them.Genesect is in the same group.The reason it's used so much more than them is mainly because he can fit in almost any team and do it's job very well.