How do we know that? Good bat rollers are very precise about the amount of pressure they apply to achieve maximum performance and they do it very uniformly. I don't see how anyone could be as accurate by hitting balls.
A hitter's performance is more than how far they can occasionally hit the ball - it's also how consistent they are getting strong hits. I'd say a rolled bat also provides more consistent performance which aids the hitter.
I wish we could do the "Pepsi Challange" in this instance, but it would be an EXPENSIVE experiment.
Maybe we could get Greenmonsters to buy me 10 brand new CF7's, 9 of those I could break in over a couple of months hitting in the cages, 1 we could send off to be professionally rolled. It would be extremely difficult to dang near impossible for anyone to distinguish the rolled bat ( performance ) vs the other 9.