As I said, there should still be an Uber tier, but they should also be grouped in with other Pokes since the other tiers are based off usage and most Ubers can be considered NU.
As far as OUs go, most are pretty good, but they go UU due to some having significant weaknesses, as well as many trainers considering them "too strong" for "real" competitive battling, much like the Uber class.
And if you don't understand yet why Smogon tiers are becoming inaccurate, you must not have read what I've said. To put it simply, Ubers need to be grouped like all other Pokes are, based on usage, but still have the stat-based Uber group. And OUs that have gone UU for a long time due in part to strength and due to them being classified as OUs, they should be considered UU. If there are tiers based on usage, they should be based on the usage of Pokes as it is NOW, not as it was in the past and usage tiers should include all 493 Pokemon, not just those that aren't considered Uber.