Genesect is one of those pokemon that look real good on paper but I guess are just average during actual battles. The team that I'm using right now looks pretty weak to Genesect, as each one of them can be OHKO'd by a +1 SE move. However, the reason why Genesect isn't fit for Ubers is because it relies so much on choiced items to work effectively. Genesect really just isn't fast enough to pull off an effective offensive set that poses pressure against opposing teams, so it usually carries a scarf to remedy that problem. Then, it gets the speed it needs, but it loses its ability to truly use its wide coverage- and although it is a great U-Turner it is worn down very quickly by Stealth Rock. I've seen RP sets, yes, but it pretty hard for Genesect to set up enough boosts to sweep without it being crippled or KO'd. And although it gets Download, it's still kind of weak, and definitely can not be compared with the behemoths such as SpecsTios or Bandorus.
I see your point, but I'd argue that Genesect is much better than just "average". The way Genesect plays, it can play many different roles, not just the scarf set everyone is hyping about. Specs / Band variants can be sent in and are instantly at +2 with the right boost from Download, coupled with Genesect's great offensive stats and exceptional coverage, not a lot really wants to switch into that. Rock Polish Genesect murders offense, while the bread and butter scarf set easily fits onto practically any team. But yeah, unlike Latios or Landorus, Genesect's main role isn't wallbreaking, unlike the aforementioned mons and with a Download boost it hits just as hard and even harder than both with a Choice item. You're also forgetting that Genesect isn't Pursuit weak, has very limited counters, isn't as priority weak and has access to U-Turn. Latios has solid counters in Jirachi and Tyranitar, but what does Genesect have? Heatran is considered the main counter to Genesect, but Genesect can viably run Hidden Power [Ground] to beat Heatran while not worrying about losing coverage -- that's what separates Genesect and Latios. It's also worth noting that Genesect can actually U-Turn out of anything that wants to switch into Genesect, turning your Genesect counters into complete liabilities. Given that U-Turn is running on pretty much every set except Rock Polish, Genesect can essentially disregard it's counters, because if you're running some sort of offensive partner with Genesect that beats its counters, then it's effectively uncounterable. Latios cannot simply bypass Jirachi or Tyranitar so easily, and needs more than one switch in to do so. This is why Stall has such a terrible time in this metagame, because everything that wants to switch into Genesect is easily beaten by something every team will have some answer for. (Genesect + Dugtrio, Genesect + Magnezone, Genesect + Keldeo, etc).
I think it's also worth mentioning just how Genesect affects the metagame as a whole, what Genesect is doing exactly. Well, like I said earlier, Genesect can fit on any type of team. Genesect can act as a failsafe Pokemon for any team due to the plethora of sets it can run. It can work on stall because stall with generally appreciate some form of offensive to break through certain walls. Balance appreciates a lategame sweeper to benefit from hazards. Most importantly though, I've found Genesect to work the best on offense teams. The way Genesect plays, it forces so many switches, even when your opponent knows your set. Scarf Genesect is the best user of Choice Scarf in the tier imo, and does so many things. The aforementioned free switches it gives on offense are great when you will likely be running some sort of setup sweeper / choice band/specs users alongside Genesect. Genesect is also a fantastic scarfer in general. Given how easily it can run that BoltBeam + U-Turn + Bug Buzz / Flamethrower set, you already have unresisted coverage coming off base 120 offenses. Genesect is not priority weak (Bullet Punch, Extremespeed, Ice Shard), Genesect has a useful Dragon resist, and it synergises so well with a lot of common 'mons you'd find on offensive teams.
You also go on to say about how to deal with Genesect, and the way you've listed to deal with it is hardly reliable. You get Stealth Rock up against it, great, it dies in 8 switch ins. That doesn't exactly hinder Genesect, and it isn't stopping it sweeping. Even common hazard setters (Deoxys-D, Ferrothorn, Forretress) have a bad matchup against Genesect, so you really can't promise hazards 100% of the time against teams using Genesect. I'd agree with you when you say you need to know the set to effectively deal with it. Given Genesect has unresisted coverage, you really need to know all of it's coverage moves before switching into it. I've found myself in situations where I'm against a +2 Speed Rock Polish Genesect, and it can sweep my team if it has Thunderbolt over Flamethrower or whatever. The variation of coverage moves really sets it aside from any other sweeper, because even a simple Life Orb 4 Attacks Genesect has no safe switch ins depending on it's coverage moves, and that's something you need to scout for. Losing Flamethrower means Ferrothorn can live a hit and Thunder Wave you, losing Thunderbolt means ~65% Keldeo can switch in against you and live a hit, losing Bug Buzz means Reuniclus can use you as setup fodder. As for Genesect's position in the metagame, I'd say it's definitely one of the best (if not, THE best) Pokemon in the tier right now. It threatens literally everything and when you get to the point where some Pokemon have to run 4 Special Defence EVs or whatever to check Genesect, you know it has a big impact and is something every team should have some way to deal with it.