Battle Revolution had it's own Surf Pikachu. The algorithm to check each Pokemon wouldn't be tough, but there are few legit ways to have a Surfing Pikachu, and none of them could be transfered with the move intact in a legit way to B/W/B2/W2, as to migrate the Pokemon forward the HM Move needed to be unlearned regardless of it being from an event and not taught via an HM. The game does not record how you learned a move, it only records that the move was there. That was the point I was trying to make, and why checks should not slow things down.
Think about how long a trade takes to go through. That it about how long I would expect a transfer to Pokebank to take for each Pokemon, including any hack checks. I think you are suggesting that people bulk uploaded their whole save files up, which I doubt is how the transfer works.