I've finally found something I disagree with you on (well, at least something major).
First, your numbers in the OP are a little off. If that big chunk that became the moon had not been bashed away... Well, you didn't adjust for that.
Second, we (humans) do not know how the moon came about for certain. Sure, there's some great theories, some of them with a ton of data backing them. But we still don't know - it's the nature of science, unfortunately. If it wasn't directly observed, we can only get a guess so good that nothing else fits - at best.
Then we get into the quantum mechanical issues regarding observation, but I think the AC who replied to your "Um, no." reply kind of brought that up. Sort of. I think. Whatever, it kind of brings it up.
Anyway, if we are truly part of an observational universe, then you're partly correct. Other life doesn't exist because we haven't observed it yet. However, that also means life outside of our known sources and locations is in a super-position.
My brain hurts.
My view is that perhaps it's true there's no other life in the observed universe, but that doesn't mean there isn't any in the unobserved universe. Also, we've had the technology (just not the gumption) to build colony ships for a while now, and we've not done a thing with it. Perhaps that's the fate of all intelligent life?