Let's go step by step here.
France has a very large immigrant population, which is true. But why exactly does that fact give them an advantage over other nations in Europe in regards to soccer? Germany has a bigger population than France and as we know, Germany also has a lot of players that have an international background. Often times they are half Turkish or at least still have a Turkish passport. What exactly makes the difference here in your opinion? I am not saying that France doesn't benefit from migrated players, they do. But Germany does as well and is much worse than France right now.
Ligue 1 emerged as one of European top leagues you claim. I ask differently: how many top leagues does Europe have in your opinion, which of them is France and where was Ligue 1 before huge amounts of money were spent on PSG?
Germany has a population of around 3 million Turks, if I am not wrong. And there are players like İlkay Gündoğan and Mesut Özil who have dominated the football scene in Germany. But France still has more number of migrant origin people (maybe 4-5 times). And another factor is that most of the migrants in Germany are Turks, Bosnians, Afghans.etc and they are not that well known for their football skills like Congolese or Ghanaian immigrants.
I am not that familiar with Ligue 1. Before players like Neymar, Kylian Mbappé and Messi were signed by Paris Saint-Germain, I hardly ever followed any of the matches in Ligue 1. I guess it was at a lower level when compared to EPL or Serie A. But now Ligue 1 is one of the top leagues.
You haven't been wrong when you said that France benefits from players that could in theory also play for another country, mainly African countries. But immigration is now an integral part of the presence even though politically there have been issues as to how this immigration came to happen in the past. But I think we would go too far back if we still keep judging that and the players also made their decision as to what country they want to play for. From that point of view it's all good. But that advantage still has not led to France being the champions all the time. They are only ranked 6th or share 5th with Uruguay and Argentina, Italy, German and Brazil are in front of them. But right now they have a huge pool of talent, which is not normal I guess that a national team has access to so many resourceful players. Lucky France!