Well except Vibrava is terrible outside of Defogging and having mildly passable bulk. Mandibuzz and Quagsire are both mildly decent in OU and have decent niches, whereas Vibrava's niche is extremely minute (hence why it's D-).
And on the matter of Volt Switch+Typhlosion core being an issue. I don't think it should mean much when banning Heliolisk. If Heliolisk proves itself to be banworthy as a Pokemon (which, imo, it is), then we ban it. If Typhlosion proves to still be an issue after this test, then we can just suspect that thing too. Suspecting Typhlosion afterwards wouldn't hurt anything except for it having to get an RU analysis despite being completely useless there.
And I do think that Heliolisk is banworthy. The thing with it is that it gains momentum far too easily with its fast Volt Switch, and it packs quite the punch with its good power and coverage with LO. It has a good secondary STAB in Hyper Voice which lets it do reasonable damage to things that resist Volt Switch. More importantly is that Heliolisk can easily smash Ground-types like Rhydon and Seismitoad with Grass Knot or Surf so it's really hard to stop it from just using Volt Switch easily. But what really makes Heliolisk such an unhealthy presence in this tier, in my opinion, is that it can provide momentum with Volt Switch while simultaneously being a powerful attacker (I believe FLCL brought up this point earlier in the thread). Heliolisk does more than provide its fast Volt Switch-it hits reasonably hard and has great coverage, so it can also put in a lot of work against slower teams, especially when things like Vileplume have been weakened (which isn't too hard because Heliolisk can just spam Volt Switch until that's the case and constantly resort to other teammates to REK). I understand that the Volt Switch argument applies to other Volt Switch users, but Heliolisk has Dry Skin and a Normal typing which allow it to take advantage of common stuff like Feraligatr and Mismagius, which is pretty darn huge if you ask me. Heliolisk also has more power and great coverage. Basically, Heliolisk is not an unstoppable monster, but it has little risk and so much reward.
I don't have much to say on Mega Steelix since so many people said what needs to be said. However, I will make the reasons I think it should be banned short and sweet. Basically, it boasts incredible bulk, a powerful defensive typing, and great offensive power in tandem with a great movepool. Due to these qualities, Mega Steelix is a Pokemon that can fit on almost any team, and at the same time will equally give any opposing team a lot of trouble. I admit that its lack of reliable recovery means that it can't come in as frequently as it would like to, but it's so bulky and has a lot of resistances, so it can take advantage of a huge, and I mean absolutely huge amount of Pokemon in this metagame, and it will be able to deal a strong amount of damage in return. Basically, with Mega Steelix's almost universal usefulness it's a Pokemon that forces you to run a dedicated answer to it (which is really hard), lest you want to suffer disproportionately at the hands of a Mega Steelix. Mega Steelix is simply a Pokemon that pulls far more than its own weight in most games.
In a nutshell, I believe these two should be banned.
