Thanks for directing me to Romain du Roi, I’d not heard of it before!
I have to say a mea culpa on this one — in my defense, this was a paper for an introductory college design class!
Most of my sources emphasized Baskerville over Fournier, and I think my ignorance of Fournier’s existence probably led to my simply glossing over his name; some of that may have to do with the fact that all of my sources are in English, so they focus on the English type designer. It’s probable that Fournier was a larger inspiration than Baskerville, being French and quite the innovator; additionally, he also developed a point system which likely inspired Didot’s own. However, the influence of Baskerville’s typeface in Europe was enormous and far-reaching, so it’s likely he pulled from that as well.
An extraordinarily large number of sources credit Didot as an inspiration for Bodoni (my specific sources are in the bibliography at the end of the piece). Because my research was on Didot specifically, I didn’t read up on Bodoni much, taking the multitude of sources repeating the claim at face value. Upon further examination, I would say it seems less that Bodoni took from or built upon Didot than that he was simply inspired by the same individuals and innovating to keep up with the aesthetic of the times, resulting in similar typefaces — especially considering that despite claims that Bodoni made his typefaces “30 years after Didot,” Bodoni was actually older than Firmin and began experimenting with creating his own type around the same time, if not earlier, than Firmin. The comments on the Met Museum’s article I linked to above actually go into detail about all of this quite nicely! I wish I’d seen that piece when I was researching my paper.