The idea with bringing back Messi is that you can maybe win the league again next season. If you can bring him back for a good wage, then it's simply the pragmatic option for a club in our position.
Sure you'd try to sign Leao, or Osimhen, but everyone with some logic in his brain can see it's not possible, and if you look at free agents next summer, Gundogan and Messi are gonna provide impact in La Liga for sure.
These are old players but with a lot of technical quality on the ball. Something which we have lacked this season. We aren't winning CL anyway next season, so I'd be open to maximizing our chances to retain the title in Spain.