I'm not trying to demean the suspect test system or anyone's personal opinion on rain in the metagame, but for us to test weather after coming this far since BW's official release (and with the recent announcement of Gen 6), is just a little too late. Yes, Politoed is amazingly powerful but cannot retain its bulk if using a more offensively orientated moveset, so for example it then becomes noticeably vulnerable to Tyranitar's Pursuit.
Cocoon, you could say Landorus affects everything. You can't be certain its the Rock Polish or Substitute + 3 attacks Landorus. The two main checks to its special set (Celebi/Latias) can suffer from U-turn, and the physical checks are OHKOed by its special set. If used sensibly, you only need one turn to set up Substitute/Rock Polish and you're guaranteed to KO something. The same could also be said for Sand Stream in that it affects everything.
Speaking of which, Sand may have struggled for a brief glimpse in OU after Excadrill was banned, but soon recaptured its glory with the infamous "VolTurn" strategy which fashioned the same six Pokemon on a daily basis.
We don't ban things in an attempt to nerf a strategy completely, however we do try to dwindle and calm its widespread impact said "suspect" has on the metagame as a whole.