So I think anyone who knows my general perspective on tiering will know my opinion on this. The only generation where a healthy environment cannot be found in either ubers or some derivative thereof is gen 1, primarily because you have a grand total of one option (mewbers) that isn't ubers or ou, and we all know Mew's borked as well.
Gen 2 is great without any bans. There are a host of different strategic options to try and matches can span a wide variety of different dynamics.
Gen 3 is summed up pretty well by TIN- broken checks broken. Looking back on the Ogre suspect I realise it wasn't quite broken in the context of Lati@s being a thing, but there are practically no reliable checks to it beyond that. At least one of Lati@s is an absolute necessity, which by definition makes it broken, but I can totally see the argument that in spite of that the tier is healthy, as Ogre is sufficiently negated by Lati@s so that it doesn't make an excessive impact. This one's really dependent on what standard you expect from a tier. The more I think on it, the more I realise that my role in the Ogre suspect was a bit of a mistake since I think it's important to identify whether or not a metagame is healthy before banning anything, even if it's technically broken.
Gen 4 idk, need to play it. Strongly doubt that it's impossible to create a balanced tier before arriving at OU though, there's just too many pokemon and broadly speaking ubers has a great
Gen 5 is great. Firstly, to address the stuff Troller mentioned, I don't see EKA as being broken given that it (usually) doesn't have any recovery, lacks the raw power to muscle through many of its checks and brings nothing but a bit of revenge killing to the table defensively, while Kyogre's Water Spout is greatly limited by the abundance of hazards in the tier. Secondly, I don't know where I was going with this =P
Gen 6 I think our 1U tier is pretty great, tbh I'd rather see fewer bans than more. That said, I definitely think that for the foreseeable future, at least some bans will be necessary- MRay is obvious, but also stuff like Geomancy and STag I don't think are healthy