Yes keep dreaming whilst you day sleeping
Messi plays the same standard he did all his life in the La Liga & yet the trophies have dropped post Iniesta & Xavi. Ronaldo scores the same amount in the La liga as Messi always has done because its a very poor league which acres and acres of space for attacking players. Ronaldo if he stuck about at Real Madrid like Messi sticks around at Barcelona - Ronaldo would still be doing what he always done because its just way too easy..
Only time Messi had to adapt to a team that he didn't grew up from the age of 13 and with growth hormone injections - he failed with Argentina except for Olympic medals. So I highly doubt why Messi would be doing wonders for Juventus (especially when he can't play with his partner Higuaín in a national team anyway), never mind teams like Bournemouth or Udinese
Would he still be good? For sure. But absolutely no way would he have the ease of playing for Barcelona and playing with the legendary Barcelona players and those la liga teams where he gets 59+ goals per season.