Politoed is no longer a mediocre Pokemon. He is now a top-tier support Pokemon with arguably the best ability in the game, with the exception of the banned Moody.
However, I will state again that if something must be banned in combination with Drizzle, there is no reason whatsoever for that something to be the entire Swift Swim ability. Such a ban is not justified, and there are better alternatives.
Politoed is a top-tier support Pokemon because of Drizzle support for other players, and in Ubers, would be outclassed by Kyogre in every way. Politoed himself is nothing special, is what I meant.
And what are your better alternatives? Banning the Drizzle + Swift Swim combo lets you still use Drizzle for other Rain things, and still lets you Swift Swim with manually set up Rain, without removing either ability outright. In quelling the major Swift Swim threats (Kabutops, Ludicolo, and Kingdra), perhaps we also hit some Swift Swim users who weren't particularly overpowered, but it's better than outright banning those Swift Swim threats, banning your Rain inducer altogether (which would cripple every other Rain team that's not focused on Swift Swim), or banning certain combos; for the last one, in my opinion, if we start allowing certain pokemon without certain abilities or moves, that opens a can of worms for banning other combos and I don't know if that's a good idea.