If Zidane accepts PSG's offer then this is the biggest good news for PSG. Because they have an extraordinary squad, the squad has no shortage of talented and star players. Their only shortcoming was the lack of experienced coaches. PSG has failed to improve itself due to lack of experienced coaches and poor match strategy. If Zidane takes charge of PSG. Then maybe PSG will be able to do better in the Champions League next season.
I cannot say that PSG problem of not winning the Champions League is caused by coaching. Pochettino is a good coach, even when he was in England, he had an average team and he did wonders with it. Having a good team he also did well, being eliminated by Real Madrid shouldn't be seen as weakness.
The problem of PSG is that they play much against low rating clubs and it affects them when they face real big teams.
Zidane to PsG will be a good move because Zidane knows how to manage big players in a team and have result.
You indicated a good thing that PSG don't have much competition in their league now. Because none of their opponents in the Ligue 1 has a squad quality even near PSG's. It is important for a team to face challenging teams to see their weak spots and try to find a permanent solution for them. But PSG are able to beat any team whenever they want so it must be feeling more difficult to compete against the biggest teams of the Champions League. But I think that Pochettino's coaching also is not that good now. Zidane might be way better for them.