... the common nature of these aspects of life on a molecular level is very strong evidence that they only originated once
Welcome home. Pull up a stump and set a spell.
Kinda, sorta, maybe.
There is another equally likely possibility is that what we see today is the surviving, more successful original line. Just as the more successful at reproducing in any given environment tends to dominate that environment it's possible that in the beginning several entirely different formats originated, but the one we see today was simply the most adaptable within the original environment and within the evolving environment.