100 bil isn't the development cost, it's the whole thing altogether, with everything. Moreover, significant part of those 100 bil, as we learned from Eurofighter, comes specifically from inefficient distributed development.
The problem right now is precisely that income from Rafale sales now both covers development costs and shows that screwing Germans with their export controls is totally worth it. All the money remains within France, all the skills remain within France.
Yes, France is fully capable of developing and fielding a modern fighter aircraft, fully competitive with what US/China/UK(did their competitive finally get ESA?) deploy in terms of capability.
That's the whole problem of it - before the Rafale export streak, France had to begrudgingly accept it(thou even then i doubt they would've pressed through with it, simply from history alone).
But after that there is only a political motivation - and given how it breaks every 5-6 years, it just pointless.