Given the Neymar-Mbappe conflict (I don’t believe it’s over), PSG will lose in quality of play during the season and especially after the World Cup (if someone starts to envy someone over its results), but this applies more to the Champions League. In the championship, their position is too strong and it makes no sense to calculate the indicators after different rounds, since the result can already be said to be known.
Neymar will have to leave in the end because he is older than Mbappe and PSG need Mbappe for long future. However, PSG has a risk that Mbappe will not stay with them too long. I believe that in the end of this contract, he will move to Real Madrid if Real still has interest in him.
Anyway, PSG need those players play together with Messi in order to win their first Champions League. Neymar has many disadvantage than Mbappe and I don't believe he will win in this conflict. In general, Mbappe can have more contribution in goals than Neymar but with support from Messi, Neymar won't be beaten too easily. I don't think too many players will like a player like Mbappe.
The battle of egos between PSG forwards is nothing new, nor is it likely to come to an end soon.
I feel the contract given to Mbappe is time bombing that would explode and leave PSG plummeting. The Management and coach needs to step in to resolve it now. Before it shows again during crucial games.
Mbappe does not have bad thinking about Neymar because of unprofessional of Neymar in recent seasons but it is also because he thinks his importance in PSG becomes bigger with time. PSG has responsibility here by giving Mbappe too many privileges.