"Sorry, common ancestry means just what it says. That all lifeforms on earth had a common ancestor. How this ancestor came into existance in the first place does not matter a lick to the theory of evolution."
You missed the point entirely. The only reason why evolution would posit a universal common ancestor was because the theory is excluding other events that would create new ancestors. We have no direct evidence for a single ancestor, therefore it is either (a) a spurious claim, or (b) a deduction from something else. If it is a spurious claim, then it needs to be removed as a proven entity. Really, though, the reason it is positted is that the theory of abiogenesis used by evolutionists exclude life from occurring more than once. However, if evolution removes abiogenesis from its dogma, then it loses universal common ancestry as well.
What about the 16S rRNA phylogenetic tree?
Conclusion is completely unrelated to premise:
a. abiogenesis could occur more than once, and lead to non-common ancestory
b.A divine spark could occur only once, removing the need for abiogenesis, but preserving common ancestory.
The two phenomena are not linked, except perpetually in the minds of those who illogically argue against common descent by disputing abiogenesis.
The evidence for common descent in numerous correlating fields of modern observation is so strong that it has even been accepted by the leading science-qualified lights of ID such as Denton, Behe, and Dembski.