Joan Collins was never statured in the way some of her era were -- but she emerged during the end of the "golden age" as a Fox contract player and minor movie star, a contract she lost when Fox was slashing costs due to CLEOPATRA overruns.
Afterwards, she did a lot of guest shot TV and smaller British movies and became more of a secondary celebrity name in the UK than she ever did in America -- until DYNASTY.
Tracey Scoggins became slightly notable playing Joan Collins' niece on DYNASTY, and I'm not sure what else.
I mean, neither was very famous in the States before the '80s, and didn't maintain a very high profile in America since then either. Even in her lowest, Collins has always been more famous than Scoggins, but that's not saying much.
I did think it was ironic when they placed Bruce Jenner's head on Stephanie Beacham's body when Caitlyn looks much more like Scoggins.