I agree 110% with Ryan. There are all sorts of converging studies, based on more or less simple models, converging maths and genetics, to say that we (meaning by we, anyone with some European ascendancy, which is I think the case of over 99,9% of WikiTree profiles) are all cousins before 1400, and have basically the same set of ascendants around 1000. The difference is just between those who can document it and those who can't.
I rarely venture before 1700 myself, and only for birth dates of people who died after 1700. I think it's enough to find common cousins with anyone here, and it's enough work. I have more than a hundred ancestors back in 1700, each with hundreds if not thousands of descendants, enough to fill a life of a genealogist through a period mostly well documented by public sources.