Messi's performance this season was not bad at all and considering the current situation of his team where they are unhappy with players and their coach, still, Messi's performance was well enough for PSG but the problem with PSG fans in they are expecting to see Messi performing much better than this and for any mistake from their team they just blame Messi.
What's the point of blaming a Messi, and I think it's a very funny thing if the fans only blame a Messi who basically always plays pretty well in the team he's defending now. Because the good and bad of a team depends on whether or not the people in the team are solid and that also includes the coach, so it is very inappropriate and very funny to only blame one person whose profession is a player.
Some club owners think that they can win trophies by buying the best players in the world. And when they do that, they expect these players to perform magic and win these competitions. Most times quality players don't guarantee success, the case of Chelsea is an example. PSG's main target is the Champions League and any top player or coach that fails to help the club to lift the trophy has failed. Messi was bought because of the Champions League and he has failed in the sight of the club management and fans. Maybe the club has now known that a team of United and diligent players is far better than a disunited team of superstars.
Messi might not also find satisfaction in Barcelona because the club has built a new empire ruled by certain key players. His coming back might bring disaffection, except he is willing to be loyal to the new order.