It also had the issue I've noticed in a few historical novels recently: a failure to mix in the (obviously thorough) research sufficiently, resulting in an unconvincing portrayal of the past which had one of the women explaining the recent developments of the suffrage movement in a love letter.

Oh yes, this exactly--too often I think it's a sign of insufficient research, because, look, they know these five things and they have to shoehorn them in somehow! So the book ends up being generally ahistorical but with these weird historical infodumps, rather than having more thorough research underlie the whole narrative and style.

This sounds like a fascinating concept for a book, and I'm sorry to hear it didn't come through for you!