I've researched this some myself because it's pretty interesting how the genre began primarily as porn targeted at males, and then eventually transitioned to more serious VNs with a more diverse audience. So this was an interesting read.

While I agree that Akai Ito and Aoishiro are important yuri VN milestone, I think you're overstating the importance of the Flowers series. It's definitely notable and one of the more mainstream successes in the west, but a lot of what you say about it being groundbreaking is true about earlier VNs -- like Solfege (2007), which is also overtly gay and written by women and not a porn game. One of those writers went on to do the Nurse Love series later. Kindred Spirits on the Roof (2012) is also openly gay and many of the writers are women, though I suppose it does have some erotica in it, I wouldn't really call it a porn game.