But there's no real evidence to suggest Messi would have struggled, quite the opposite infact.
Firstly similar type of players went to the PL and smashed it and each and every one of them were inferior to Messi by a distance (stating the obvious). David Silva, Juan Mata and Sergio Aguero the prime examples. And not only that he has in general destroyed the PL sides he faced in the CL. I mean West Brom, Stoke and the like succeeding where United, Arsenal, City, Chelsea (he may have took a while to score past us but he ripped us apart in some of games prior to that despite not scoring), Spurs and Liverpool have all failed? I guess everything's possible but it's highly unlikely!