There are other ways for other Ligue 1 clubs to attract investors by proving their success in other, more impressive competitions like the UEFA Europa League.
Only then can clubs like Monaco, Marseille, and others have a chance of attracting significant funding from investors.
However, other clubs have also failed to compete for Europa League titles, making them seem unattractive and making investors hesitant to invest.
If these Ligue 1 clubs were willing to think realistically and strive for greater funding, I believe there would be a positive change in their performance.
Clubs in Ligue 1 can not compete fairly with PSG in most of seasons because they don't have similar financial budget like PSG and they often sell their best players to PSG or other big clubs in Europe. PSG oppositely have bought best players from French clubs and other clubs in Europe and these opposite club development and player transfer strategies make big differences in competitiveness of PSG and other French clubs.
PSG only lose their domination in Ligue 1 if their finance has big problems and they stop purchasing star players. In the near future, it won't happen and Ligue 1 will continue to be dominated by PSG.