Uh, the reason he most likely WONT use a crobat is as follows: Because it doesn't help the team. Sharpedo is even worse, it's water type without swift swim, which means all its going to add is an electric weakness. Rough skin can't help sharpedo survive jack, it'd be dead by then.
Also, I highly doubt you spotted the ninjask error, because, as the hindsight bias, it's easy for someone to say "Oh, I knew it all along" when they actually didn't really know it.
Either way, Frosty, Trode works. Swift swimmer my butt, when did you plan to use rain dance when you had trode and Dactyl out? If they send out swift swimmers it'd only be when you have at least 1 swift swimmer out yourself, and as long as you add a bit more speed EVs, your swift swimmers would be faster than their own >=(
(Losing the touch, are we? :p)
