But I feel this logic completely ignores "inbreeding" even if it's to the 5th, 10th or 20th degree. It's like seeing a human as the root of its ancestors tree,

But I feel this logic completely ignores "inbreeding" even if it's to the 5th, 10th or 20th degree. It's like seeing a human as the root of its ancestors tree, and saying that this tree is well balanced all the way to the nodes at depth 100 or so. But surely it's not a well balanced tree, more like a directed graph with many sideways connections. There could be multiple clusters, lineages, more or less narrow, coming from the bottom and reaching the top.