I work with modern French (my focus is on the Maghreb), so I can't speak to early modern French. However, two years of French at the undergraduate level and 9 months in France, as well as a paper drawing heavily from archival work in France and French secondary sources, did the trick. I got into my (decent) PhD program without an MA. Mind you, I also put a lottttt of time into French on my own. It was my hobby. French reading, youtube videos, speaking with natives on Italki, etc., are how I spent a lot of my time after work. I should also say that I'm a heritage speaker in Spanish, and that did help in understanding French at the structural level.
Good luck! It's fortunately a language that has a lot of learning resources out there.