I firmly believe that Sneasel is broken and unhealthy for the XY LC metagame, though I'm unsure if it meets the requirements for the quickban. I'll go point-by-point here:
1) Is Sneasel broken?
Sneasel has proven itself to be the single most threatening thing in Little Cup at the moment. There is no other Pokemon in the tier who can just come in and start smashing without any set-up like LO Sneasel can. Getting it in on something it can OHKO is, at the worst, a guaranteed loss of a Pokemon, or at the best, a now-Evioliteless check to Sneasel who can no longer switch in anymore, making it a 2HKO the next time Sneasel comes around. There is a lot that Sneasel can OHKO in this metagame thanks to how powerful the Ice-type is in LC. A large percentage of the top threats in LC (also going a bit into 5th gen threats here) are weak to either Dark or Ice, including Murkrow, Misdreavus, Gligar, Honedge, Lileep, Tangela, Yanma, and Abra. Those that don't are still not safe, since Knock Off cripples anything that switches in. Pokemon like Porygon, Chinchou, Lickitung, and other defensive Pokemon that could take a hit before now find themselves unable to switch into anything anymore, and are practically useless. Grimer and Shellos are the two Sticky Hold users in LC that come to mind, but neither resist Dark, meaning they will just keep eating that increased Knock Off damage until they are knocked out. Ice Shard finishes of weakened Pokemon while also destroying revenge killers like Scarf Murkrow and Gale Wings Fletchling. The Swords Dance set is something I have yet to see on the ladder, so I'll refrain from passing judgment on that for now. On the defensive side, 55/55/75 defenses are very good for a sweeper with as much power as Sneasel, meaning that it can take powerful resisted and neutral hits and still have enough HP left to knock out its attacker. As an example, LO Murkrow's Brave Bird does not OHKO Sneasel at full health
Another important thing to note is that Sneasel entirely lacks counters. People in the past have said the same about stuff like LO Murkrow, but that at least had a niche counter in the form of Aron. Nothing can switch into Sneasel because of Knock Off, and thus your only hope of beating it is with multiple checks. Timburr stands out since it has 4x SE priority and a resistance to Knock Off, and Scarf Mienfoo just barely outspeeds Sneasel for an obvious OHKO while not being weak to Ice Shard. Swirlix can beat Sneasel the first turn it's in because of the Speed boost from Unburden (assuming Sneasel used Knock Off or Ice Punch to trigger the Berry Juice), but after that it gets iffy. Stealth Rock hurts Sneasel, but since it crushes Ghost-types into the ground, spinning on a team with Sneasel is very easy to do. Unless, of course, the other team has Sneasel, since it also happens to rip apart all the common spinners in the metagame. Everything else in the metagame simply stands no chance against Sneasel's power. This is why I believe Sneasel to be broken.
2) Is Sneasel making Little Cup not fun?
I don't know about you guys, but I personally find facing a Sneasel in almost every match to not be fun at all. Furthermore, I also find using it to not be that much fun either. After all, there's no real strategy to using Sneasel. You just come in after one of your Pokemon has either fainted or used U-turn, then wreck something. Nothing is immune to Knock Off itself, so there's no risk in using it unlike something like Mienfoo's HJK. As such, the key point I'm trying to make here is that Sneasel is way too low-risk for a high-reward, which makes being on both sides of it boring and unfun. Unlesss you really don't have a clue what you are doing, Sneasel sweeps too easily to keep it in the metagame.
3) Is a combination of 1 and 2 deterring individuals from playing Little Cup?
Obviously people are still playing the tier, and I think there are plenty of people who have fun using OP stuff, so I wouldn't say it has made a huge impact in deterring people from playing. That said, I question the importance of this point considering that not all players play the same way. Some players love to abuse OP Pokemon, such as Scyther. Nobody questions Scyther was broken, but for every player turned away by it being in the tier, I'd bet there's another player itching to take it out for a spin. Even I sometimes find it fun to just piece together as much broken stuff as I can on one team and just see how far I can get on the ladder.
As such, what I'd like to ask is: Is Sneasel deterring serious players from playing the metagame? I can answer from personal experience that yes, it is a detriment to the tier to have such an obviously broken Pokemon in the metagame. Outside of having other engagements, my main reason for not playing much Gen 6 LC is that I don't find it fun to play Sneasel Wars, and I also don't want to become adjusted to the metagame in its current state. I know that there will be a few Pokemon that will be banned eventually, and I personally would rather not get used to using them or facing them. Some say that has little effect on them, but for me personally, I am put off by huge sweeping changes like that which might occur once suspect testing gets underway. In terms of the original question, I don't think that Sneasel has truly prevented too many users from playing, I can say that some serious players such as myself are indeed put off by having Sneasel in the metagame.