Showing comparisons and similarities in DNA does not automatically equate that everything spawned from a common ancestor - Bad wolf
Yes that is correct. The evidence for common ancestry in our DNA is far far more compelling than simple sequence comparison. I have described quite a few in this series of threads including pseudogenes, ERVs, ALU elements. Here is an extract from #3 ...
Imagine you are teacher with suspicions that some of your pupils have been copying from each other. Comparing the correct answers in all of their assignments might not provide conclusive evidence. They could simply claim they had all carefully revised the same textbooks so it shouldn't be surprising that they all gave the same answers. The way to prove there has been cheating going on is to examine their mistakes. There might be only one way to answer some questions correctly but there are almost limitless ways to get it wrong.
By examining a number of identical mistakes you could even build up a family tree of plagiarism and show who wrote the original essay and who copied from whom.
In a similar way geneticists have been able to confirm the evolutionary history of humans and other species by examining errors in our DNA.