If they wanted to run projects like PSg in the premier league they had to spend much more money because in the premier league, there are many ort rich teams and there is a closer race between other teams while in the French League, they could have easier days, if they were spending this money in premier they could even lose the top of the table easily.
That is exactly the point and that is why I am not a big fan of picking a league that is inferior and then invest a billion and celebrate the team for winning the title on a yearly basis. Not a lot of people are truly excited when they can watch Neymar, Messi and Mbappe play against Troyes. But what if they hypothetically be playing for Newcastle instead and people get to see them to play against Manchester United / City, Liverpool, Tottenham, Chelsea etc. Having those three guys play for the Ligue 1 title in the same team became very boring over time. Everyone was waiting for half a year to pass until the knockout games in the Champions League finally began and if PSG got eliminated early, then the season was essentially over.
PSG spent a lot of money and signed several star players. Even then their performance was not good. Even though the Ligue 1 teams are not very strong, the PSG team cannot perform well. Even PSG spent a lot of money to win the Champions League title. But their performance in the Champions League was worse. Even though they have a lot of money, PSG management can buy star players even if Messi and Neymar leave the team. We will see a lot of star players in PSG's squad next season as well. However, Ligue 1 is not very competitive. And I think the Newcastle team is much stronger than PSG right now. Because the Premier League is very competitive. The standards of Ligue 1 teams are much lower than Premier League teams.
PSG's spending spree, in contrast with their subpar performance, seems as mismatched as a bird at a fish party. Messi's situation in PSG is a stark reminder that the best of players can struggle under unqualified management. Galtier's public admission about struggling to tap into Messi's potential exemplifies this issue. The role of a competent coach, as you aptly pointed out, cannot be undermined.
It's indeed true that Ligue 1 falls short in terms of competition when juxtaposed with the Premier League. While PSG may dominate their domestic league with their galaxy of stars, the real test of their mettle comes at the continental level, where they've been underwhelming. Perhaps the likes of Newcastle are indeed in a better position to compete given the rigorous competition they face week in, week out.