I agree with you. We all know Mbappe was the most important player in PSG's squad. There is no doubt that Mbappe was PSG's leading scorer. But I don't think PSG can dominate Ligue 1 without Mbappe. Without Mbappe, it may be difficult for PSG to perform well in the Champions League. However, it will not be difficult for PSG to dominate the league.
PSG is a very rich club. And they never skimp on spending money. Moreover, PSG coach Luis Enrique is very experienced. Luis Enrique will certainly take whatever steps are necessary to strengthen his squad. And Luis Enrique will get all financial support from PSG management. So I believe Luis Enrique will be able to keep the performance of PSG team stable in the next season as well. And PSG will dominate Ligue 1.
In terms of scoring goals it may be true that the he left of Mbappe will affect the number of goals that PSG will produce each season, but in order to dominate Ligue 1, I don't think it will affect the presence or absence of Mbappe There are still several other players that Luis Enrique can rely on and maybe they will also look for a replacement after Mabppe left for Real Madrid.
This financial support is what makes most people not think that PSG's dominance will be taken over by another team because they can still find a replacement to fill the void left by Mbbape. Moreover, Luis Enrique is also quite an experienced coach so these two aspects will be added value for PSG to continue dominating Ligue 1.