Better than Muhammad Ali?
Better than Michael Jordan?
Better than Diego Maradona or Pele?
I immediately discount 'provincial' or 'non-world' sports participants - cricket, ice hockey, gridiron, AFL, rugby union, rugby league, baseball, etc, etc
Messi has won the Ballon D'Or 7 times, more than double anyone else except for Cristiano Ronaldo
I dont think you can compare former sporting legends (regardless of whatsport it is) with current players as technology has improved significantly as well as teams have become a lot more competitive. If you put Pele and Maradona against current Man City or Real Madrid, would they perform as well as they did back in their glory days?