As you say, the attractiveness of sitters is subjective. What's most likely catching you up is that the style of faces prized most during the late 19th and early 20th centuries is far from what is currently in style.

Just like hair, figure, and clothing, faces have fashions. Until fairly recently, the sort of woman's face that was considered beautiful had more fullness in the cheek and more roundness in the jawline — and I do mean recently, because even Twiggy, the ultra-thin 1960s model who's often credited with creating the vogue for being extremely thin, lacked the sort of hollow cheeks and prominent cheekbones now practically required today. If you look up singers and actresses from the 1920s, 1930s, 1940s and so on you can easily follow the slow transition from the smooth face with little cheekbone definition and often a larger chin and nose to the more "delicate" faces considered attractive today. (I'm so sorry for not linking to specific images — I'm on mobile as I'm away from home. I would recommend Gaby Deslys and Billie Burke for the Edwardian era; Mary Pickford and Clara Bow for the 1920s; Jean Harlow, Ginger Rogers, and Betty Grable for the 1930s; Joan Crawford and Katherine Hepburn for the 1940s … and of course these can be followed through the decades to see the subtle ways that their faces changed to fit current ideals.)

You mentioned makeup, so I know you're aware of it, but really consider how much of an effect that it has on the face, and how much the modern eye is primed to expect it to be used to smooth out imperfections. Cosmetics have existed for centuries, but in the late 19th century most women would not use more than perhaps some face powder — no rouge/blush, no lip color, no eyeliner or mascara, which means that photographed faces will look washed out and ill-defined compared to modern women.

I don't really think your basic question is answerable, because as you say, it's so subjective. I don't know whether you've already seen and dismissed Lillian Russell or Lillie Langtry, for instance, or if naming them will lead you to images you find attractive. All I can say is that the vast majority of the time when people who aren't acclimated to the standards of the 19th century share pictures of "old time" women considered beautiful, they mainly share images from about 1900 to 1915, representing early 20th century actresses/vaudeville stars like Burke and Deslys from above, plus Evelyn Nesbit, Anna Held, et al.