It’s not so bad for the time, when you consider the leads were actually cast in TOS.
From day one...Ilia is on the poster and a main character, Saavik is everywhere in II and there’s carol, III has Saavik, though not in as big a role, IV has Gillian, and V has Uhura getting her scenes, as well as strong supporting roles like Caitlin Daar and the Klingon first officer...they aren’t exactly leads, but they are way more than extras. VI has Azet Bur and Valeris. The leads are always gonna be Bill, Leonard and De, but once you take that out of the equation, it’s really pretty good for the film genre and the time. Overall, it’s only really Nemesis and Generations that let the side down, and Generations was a shopping list movie...Nemesis was such a mess in the end there’s not much that would have saved it, though you can make an argument that many key roles in it are women...Senator Thingy and Troi are key characters, if treated pretty shoddily. But this is a filme abou PICARD and DATA and everyone else is unimportant.