One of the three - Messi, Neymar, Mbappé - is superfluous. One of them has to leave. In this case, Psj will have a balance in the team and Messi will be as usual in his position. And when the enemy attacks, there will be plus one player in defense. Pochettino tries to find a balance, but he fails. And I don't think it will work out. We can expect a couple of such games in the future, when the team will not succeed.
Three players don't contribute too much for defense system and it would be serious weakness of PSG when they face with teams that have dangerous counter attacks. Bayern Munich is one of such opponents. Pochettino have to focus more on defensive midfielders and tactics to support defenders because I think he would not succeed to require Mbappe, Neymar or Messi to do defensive tasks.
Pocchettino has now arranged the PSG team in such a formation, with this formation the players of the team are completely new. So they are not being able to play well from their place. Give them time, maybe in a few days they will be able to perform better from their place. And even then if the team will not stable. Then coach Pocchettino must think of something alternative. He has to change the formation.
Messi is genius and he will adapt to the new mates, new tactic very soon. He shows some signal of good adaptation recently and I believe he will show his best after the Christmas.
About transfer, there is news that Haaland will join PSG to replace Mbappe.
Erling Haaland's agent Mino Raiola will 'request an eyewatering £43MILLION-a-year salary' for the striker to join PSG.
I don't think PSG will accept the complete loss in the case of Mbappe and they will try all things they can do to renew a contract with KM7. It would be a too dangerous team if they can keep Mbappe and have Haaland. Messi only play in Paris 2 to 3 seasons and at his age, he will have to face with downside of his performance soon. Mbappe and Haaland will be the future.