oh please , he would have been amazing at Real aswell . Imagine having him in your team with the referees on your side aswell , and with Perez influential in the bdor results every year. They would have been invincible
But in the 85th minute at 0:1, he would try to play 1-2s at the edge of a box instead of waiting for crosses/headers/rebounds/penalties in the box.
Also, with Messi, Real would have less counters.
So, it is not that simple.
You can't put any player into any team.
Look at Liverpool, they were way stronger with shitty workhorses midfielders for their style.
They changed a workhorse for a superior possession player Thiago and their game lost a bit of aggression, pace and now every ball goes through him (on the ground through the middle) which means less counters and less crosses from fullbacks.
You change one player and you get totally different attacking patterns, movements, different ratio of attacks focused on the middle/flanks (let's say from 50:50 to 70:30).
The same would happen with Messi at RM.
They would win majority of La Ligas.
For a CL, everyone will have a different take on that question.