That's a really narrow way of thinking... not to mention completely wrong considering you miss the idea of competitive play... you're essentially undermining everyone who ever played old UU with that phrase.
Old UU was different from New UU is how you should look at it. It's a completely different metagame so I'm curious why you're comparing banlists - depending on the Pokemon and Players available, you'll end up with different ideas of what is broken. To say the old UU was "screwed up" because the banlist and the metagame was completely different from new UU... I'll let you figure that one out yourself since hopefully you're capable of doing so.
First off, if you don't remember I
played old UU, extensively and was quite involved up until the point where we really started getting the plans off to drop the BL pokes. I had lots of discussions and mutual respect with Shiny Oddish, Cynthia, Age of Kings, etc. etc., who by the way haven't been around in ages for whatever reason.
And no, it's not just a matter of "difference." Pokes that were banned from UU based totally on theorymon (entei, ramparados, pinser, etc.) have now been proven to be less useful competitively than pokes that were allowed in the tier (froslass, rotom, steelix, clefable, etc.). That to me, is quite a distinct indicator that our methods for creating the old UU were ineffectual, and created a rather warped tier.
And you could see it in play near the end-- practically every team was looking to set up SR + Spikes + Toxic Spikes + Status 3-4 of the enemy pokes + rapid spin + block with 2 different ghosts (yeah, froslass and rotom were gods). I am exhagerating a bit, but I think it's fair to say that the benefit from actually attacking was so low (the offensive pokes so weak) that there was little point in actually attacking (unless you were absol, in which case nothing could stop you after platinum, but you were still gonna die in 1-2 turns and you were kinda a one man show).
I'm not saying the people who made Old UU were stupid (contrary, they were quite intelligent overall, and some I'd say very much so), but that doesn't change the fact that all the theorymonning created a tier that, looking at the usage stats we have now, does not make sense.
Yes, in a way you can say "it's just because the tiers were different," because pokemon usage is affected by what's available. IE Eruption Entei might have ripped through old UU (though I doubt it), but can't do so through new UU because of Chansey. That example was totally imagined up there, but the point is yeah-- pokemon usefulness also depends on what's around them so in a way "you can't compare the tiers because they're fundamentally different."
But it's not completely about environment. There's also the individual abilities of each pokemon. Scizor is the king of OU and that's every bit as much because its offensive abilities are really impressive, as it is about the fact it can 1hko A, B and C under conditions D. I think a couple of pokes to demonstrate this point really well recently are Lucario and Wobbuffet. Environmentally speaking, everyone up until this point thought of them as really unimpressive in Ubers, but the abilities that they actually have was shown to be really powerful in practice. Inversely, it's been a historical idea that Pinser never got any use in OU just because it was outclassed so badly by Heracross. In practice though, even without heracross around Pinser still isn't UU-- which indicates something about Pinser itself (lol, SR weak!).
In the same way, the fact that Clefable was a top UU before, and still is a top UU now while pokes who were banned are falling to NU, I think that speaks a lot for Clefable.