Thought I would chime in on genesect, please be gentle :)
I've heard a bunch of arguments for banning genesect. They generally fall under the categories 1) genesect beats x type too easily 2) bug is too strong and 3) genesect is too diverse.
Personally, I don't think the first 2 are good reasons to ban genesect. Let's just take a look at some specific matchups.
Other bug teams-Genesect is definitely very important in this matchup, but since both teams have it it isn't unbalanced either way, unless one has flamethrower and the other does not.
Psychic-Because genesect's strength is coverage, it's not actually that broken in bug vs psychic, or at least not compared to either bugs. Obviously its bug stabs will hurt but so will those of other pokes such as hera and volc. Genesect can kill slowbro better than others and the steel typing is nice but as far as stab goes genesect may or may not be good vs psychic, depending on its set, but its replacement bug could be as good or better.
Flying-In my experience this matchup leans towards flying, with sending genesect in on skarmory being bug's only way of winning. Genesect threatens almost anything on flying but in return is slower and when charizard comes in on it bug has a tough time switching in. There's a lot of depth to this matchup right now, especially the hazards, but it is in flying's favor with genesect being bug's strongest weapon, so genesect is healthy in this one. Also, while nothing wants to switch in, plenty can outspeed once it's in.
Fighting-Genesect is ok in this matchup but doesn't really define it. It does have some value as a terrakion check though. In this instance there actually isn't a coverage move that will really help.
Water-I'm gonna split water into swift swim offense, balanced, and stall (ie cancer, thank thimo not me though).
Swift swimmers tend to outspeed and destroy genesect with water moves, but outside of rain genesect with energy ball generally means something will die, since they don't have sap sipper azu. I think that's ok though since offensive teams shouldn't be judged based on their defensive potential-it's fine if nothing can switch into genesect as long as everything can kill it, and rain boosted hydro pumps will. Thunderbolt is balanced in this matchup because of swampert. Energy ball is scary but it's worth noting politoed gives a +atk boost with its 100 sp def.
Balanced isn't very happy about energy ball genesect. Unlike swift swim, it probably can't OHKO genesect, but like swift swim, it probably doesn't have sap sipper azu. Gyarados is a decent check though, and again thunderbolt is taken care of by swampert. Genesect with both thunderbolt and energy ball are rare. ("but I don't know what set it is till it kills me" ill get to that later)
Stall needs the check imo, typically the only thing bug has that really threatens stall is mega pinsir and lanturn/azumarill do a good job of checking it.
Steel-While bug has only a 40% win rate vs steel, I think it would be higher if people used genesect effectively. Douse genesect can kill literally everything on steel in one or two hits (sp def heatran can take a techno blast, especially if it gave genesect an atk boost). Once heatran is removed flamethrower/volcarona can win the game for bug. I think this is how it should be because bug's other sweepers aren't great vs steel. Steel has rocks and bisharp for defog/doublade for spin so it can cripple bug and has skarm/doublade to stop pinsir or hera sweeps, plus bisharp scares away sticky webs, so this matchup is like flying in that bug has a disadvantage and genesect is its only weapon. btw people, try douse plate :D
Dragon-I'm not too sure about this one. Ice beam tears dragon lacking goodra/kyurem a new one. Obviously the steel typing is also nice for taking outrages and stuff. HP fire checks but does not counter. I don't play much dragon so idk about how it will be without mega altaria but still pretty sure dragon won't have any reliable switch ins to genesect. Also, the rest of the matchup isn't too bad for bug either, so that justification is gone.
pt if you have flam
Ground-Something nice is the perfect 50% winrate. However, that doesn't guarantee your bug vs ground game is a 50% chance to win: it depends on genesect's set and the enemy team's counters.
Against generic ground (mega chomp) ice beam will hit everything and u turn lets genesect bounce off gastro/seismitoad, which is nice. However, the switch ins all fear a scald burn and may struggle with hippowdown or get revenged by excadrill. It's balanced unless genesect has energy ball, in which case nothing on generic ground can switch in.
Against stun's camerupt ground it's a different story. There is flat out nothing on ground that can shrug off a fire blast from mega camerupt. For its part, camerupt takes anything but douse techno blast. You may have noticed a pattern by now-it depends on if genesect has the coverage move it needs or not.
Dark-Similar to the dynamic with heatran vs steel, douse genesect wears down ttar until volc can sweep, genesect is also good as bug's switch in to mandibuzz. Like psychic, genesect's stab bug moves hurt, but other mons hurt more.
Normal-honestly does very little in this matchup, chansey/pory2 can't be exploited through coverage and you are even in danger of getting reverse swept by ditto if you have flamethrower
Fire-So traditionally fire beats bugs weak to it like genesect but if you somehow get rocks/webs up douse genesect can apply a lot of pressure since it can kill torkoal, but I don't think anybody says genesect is op because it beats fire. Even if you do have douse the sun makes it pretty weak.
Fairy-If it has scarfed steel stab fairy is in trouble, klefki and azumarill might be able to do something but certain sets could definitely pose a problem for fairy.
Ghost-Genesect doesn't have coverage for ghost, ghost users correct me but people don't say gene should be banned cause of ghost.
Electric-Unlike other bugs, genesect threatens zapdos and rotom w. But it's not exactly broken vs electric.
Grass-Grass has nothing that can switch into genesect, mega vena is fine once it's in though. But tbh bug is gonna destroy grass regardless so grass isn't that relevant to genesect being banned or not.
Ice-Ice does struggle with bug and genesect makes it worse, I'll admit. I haven't played this matchup enough to say for sure. However, if we are going to ban everything good vs ice we will end up banning half the meta.
Poision-immunity to poison doesn't mean much, but it's nice that it outspeeds nidoking and threatens everybody except mega vena. Not matchup defining op though.
Rock-Bug vs rock is actually a very interesting matchup atm, I think either can win with a good team. Without genesect this matchup would be wayyy in rock's favor.
OK, so those were the matchups, I admit I got bored towards the end but oh well. I think genesect is certainly important to some matchups depending on its set, but a lot of the matchups it impacts heavily would be hard for bug without genesect.
That brings me to the second argument-bug is too strong atm and needs a nerf. Looking at winrates and popularity bug does seem strong, but I'll let others decide if it's too strong and if genesect is the deserved nerf.
So the final point is its diversity. This is the most convincing argument. Throughout the matchups I've said gene beats x if it has y, it beats a if it has b, etc. And so while it doesn't have 4 overpowered moves that make 1 broken set (although I love douse myself) it does have a bunch of strong moves that make it strong and unpredictable overall. That is, you don't know if genesect is going to hit you with a banded e speed or douse techno blast or u turn out or flamethrower or etc etc. And that list does go on a long time. The thing is, people make that argument but at the same time cry about how download gives it free +1. Well, if they downloaded you know if they got a physical or special boost, and judging by the context of when they sent it in you know what they want to do. I'm not saying it can't throw a nasty curveball at you but don't act like you automatically have to sacrifice a poke when it's sent in just to figure out what it will do, because you know already. That's not the challenge-the challenge is stopping it once you know its set, because if the set is good vs your type you are in trouble.
As far as 4 moveslot syndrome goes, genesect can threaten any type, but it can't threaten every type