Ok, well those don't counter every defensive version.
Basically, you split it in half, (with some minor exceptions):
Milotic: LO Ice Beam on specially defensive Venusaur: 47.3-56% (Not a 2HKO)
I'll skip Moltres, because I believe it is one of the few true counters to Venusaur.
Swellow: Brave Bird on physically defensive Venusaur: 65.9-75% (Venusaur OHKO's in return with Sludge Bomb taking recoil into consideration)
I'll skip Mesprit, because it does a good job.
Rhyperior: No, EQ may be a 2HKO, but Energy Ball is a OHKO and you outspeed it.
Houndoom: The OHKO with Fire Blast is only guarenteed with SR damage as it does 90.7-107.7%
Note that you also have Sleep Powder to deal with.
So there, that's 4-5 pokemon in all of UU that can deal with Venusaur. I just don't think it's healthy and is making UU into OU by forcing people to use these pokemon or lose to the #1 used pokemon in UU.