I know leaving all the 300+ year old people out of GEDCOM imports is not a perfect solution, but believe me when I say it was worse the other way! We end up with far fewer duplicates of historically significant people than we used to.
That's why the user groups were originally formed. There were certain people, like the Mayflower passengers, who had 20 or more duplicate profiles! It was a lot of work to get them merged and the profiles cleaned up, and this work is still being done today. As long as people could keep importing duplicates of those people, the work was always sort of one step forward, two steps back.
Now, people still manually create duplicates, but not at nearly the same rate as when they could do it automatically. So that really does make a difference. A lot of people will instead see that there's already a profile, and connect to it rather than creating their own.