But what claim does ancestry truly offer? If my parents are from the UK, do I qualify for Super Citizenship there? What if those parents had only been UK citizens for 2 generations? What if it's my great-grandparents, but they were part of a lineage that spent 22 generations "building" the UK, surely an absence of only 3 generations is just a rounding error!
And US immigration policy favored Europeans, based exactly on shared ancestry, all the way up to the Hart-Celler Act of 1965. So for most of its history, this logic didn't sound alien to US ears at all, despite being a young country. It has abandoned it only relatively recently, paradoxically as it got older. In fact, with how often the US is still accused of xenophobia (despite immigration policies that will see its former 90% majority become a minority in a mere 24 years), I find it puzzling how you can make that statement in the first place.
As for your question about your grandparents, many countries do indeed recognize a right of return, but the UK is not among them, so you're out of luck: https://en.wikipedia.org/wiki/Right_of_return
Of course this does not apply so much to major corporations, but that is a different matter.