Not sure what you're asking?
"Significantly" doesn't seem to be correct. At least, not for the (GPL licensed?) stuff that's been stuck on ancient versions for many years.
Though they have (from my rough memory) made some contributions back to FreeBSD where it seemed to make sense.
All that aside, the point is that they didn't build their platform "almost from scratch".
They assembled a lot of pre-existing pieces (many OSS), then built on top of that. It's a common way of doing things.