Isco,
You probably thought the same when Bayern won the German league 10 years ago, and look now, they are with two teams in the CL final.
I agree that now, at this moment, it looks like the French league is a shit league, but in a few years, this might all change.
And to be honest, footballers' careers go up until +/- 35. If you have the option to have financial security by then OR to be a legend for some team, but don't have the financial security, I think the second option is an option worth thinking about.