Okay, you can't lecture me for lacking logic and then present multiple unsubstantiated and imo completely wrong opinions as fact.
1. Hasn't hurt the metagame at all.
Okay...so the fundamental thing we want from the metagame is diversity, yes? If stuff is completely broken, it lowers diversity because it forces you to use the few available checks etc. And yet, 99% of teams fall within 6 archetypes, all of which use the same small set of pokemon. Nearly every bloody team I've seen today was based around Genesect + a hard Heatran counter (Dugtrio on Sun and Rain, Terrakion etc on Sand). Stall is widely acknowledged to be, if not dead, then barely viable and definitely on the way out.There is NO diversity any more.
2. Easily beatable with the right support.
No. You can't beat Genesect unless your entire team doesn't care about it, in which case, your team is awful. The usually touted way is to get hazards and stop the opponent getting hazards; and yet we live in a meta in which SR + Taunt Terrakion, Mental Herb Deoxys-D and co are everywhere, and correspondingly, Rapid Spinners and Magic Bounce are also everywhere. Genesect's momentum based strategy makes it even harder to control the hazards on both sides of the field, at least without taking massive risks. What's the solution as a teambuilder? Yeah, sure, use Aerodactyl or something (lol - I should also mention that most of the faster anti-anti-leads, like Azelf, are outsped and brought to Sash by Genesect). How do you handle the abundant Rapid Spinners? Most of the time, the best answer is to use Genesect on another cookie cutter offense team, = still less diversity.
3. Any decent defensive core can wear him down and then use a faster mon to clean him up.
Again, defensive cores are harder than ever to use successfully in this metagame. I just talked about how hard it is to keep hazards against Gene-offense. Defensive teams, or even defensive cores within a team, have an even harder time of it; they can't afford to take a risk (e.g. predicting Scarf Gene's move) because if they mispredict they get swept. And the idea of a faster pokemon "cleaning it up"? First of all, even being able to bring a pokemon into Genesect and then be able to hit it is extremely rare, since most of the time it's just U-turning. Second, it can just switch; if you're outspeeding Scarf Gene, you must also be Scarfed, therefore unless you predict like a boss (which isn't a reliable strategy) you're turning yourself into setup fodder. Finally, Scarfed Mons which outspeed Genesect aren't common and are becoming less common because people just use their own Genesect instead.