By your logic you could have a team of Roar Zapdos, WW Skarmory, WW Hariyama, Roar Suicune, Roar Salamence and WW Snorlax and say 'I can counter everything since I can switch on anything and phaze it away'.
If you are not threatening the oposition you're not countering at all, and I'm not sure (didn't calc anything) but Hammer Arm from an once Bulk Up'd Rev should do more damage then a Skarm Brave Bird on the same situation, which means Skarm would lose ONE-ON-ONE, which is what really matters >_>
And no, Skarmory was never a Curselax Counter, unless it has Taunt + Toxic or Counter.
Any ADV team that relied only on Skarmory to stop Curselax would lose, same thing applies here.
Sorry for my shitty english :P