Not all star player is able to adapt with a new team and a new competition.
LaLiga and EPL has different rhythm, so there is no guarantee that Messi will be able to play as great as when he play in LaLiga.
Any players need a process to adapt and it may take a bit longer time, so I do think it is better if City look for younger player as it can be a long term purpose.
I'm afraid if City sign Messi, City will become a "one man centered" team which wont work in EPL
Yes, I still remember how Fernando Torres come to EPL and not giving good contributions. However, Guardiola know how to maintain Messi when he was in Barcelona, Maybe Guardiola already have a plans how to choose best formations with Messi in.
Maybe this. Pep and Leo got along very well even if they had some fights every now and then. In the end it is about Messi's contract which I believe is a very big one: this situation reminds me when Ronaldo decided to play for Juve, they basically got a win-win situation due to the very low taxation that Ronaldo found in Italy (that is the main reason why he decide to play there, not else).
Barcelona currently in financial crisis because of Covid maybe this is one of the reason. If we remember about this, maybe you are right if this is a win-win solutions, but now Barcelona need Messi to maintain their positions, I can't imagine Barcelona without him next season.