dredmorbius did a good job answering, but I'll put it in my words too.
My post spoke not about the existence of porn stars then, but our awareness of them today.
Their notability may be great in their lifetimes, but does not stand the test of time. Scientists, on the other hand, may not attain notability in their lifetimes, but their stature stands the test of time. At least in the case of some great ones.
How many American Presidents do you know from the Renaissance period? How many quantum physicists do you know from Medieval Europe? They obviously will never stand the test of time!
Your conclusion is perfectly fine for the reasons that dredmorbius says, but that wasn't what he was disputing. He was disputing that your specific argument was so obviously faulty that it is just absurd.
My post spoke not about the existence of porn stars then, but our awareness of them today.
Their notability may be great in their lifetimes, but does not stand the test of time. Scientists, on the other hand, may not attain notability in their lifetimes, but their stature stands the test of time. At least in the case of some great ones.