#4 Defensive problems for the opposition
It has already been proven difficult for teams to stop either Ronaldo or Messi when they are playing for Real Madrid and Barcelona respectively. If they were to play for the same team, imagine how big a headache it would be for the opposition coach.
Both of them are unstoppable when they are in peak form. Man-marking would seem to be the obvious option but then again, there are very few defenders in the world who can actually mark Ronaldo or Messi.
And when they would play together for the same team, who could possibly stop them? Even if all the 10 outfield players of the opposition manage to stop the two, there will be eight others in Ronaldo and Messi’s team other than the goalkeeper who could be easily be fed by either of the two.