The point is surely that no search engine is very reliable as a source for standard usage, because there's so much bad writing and bad English out there. It helps somewhat to limit your search to only site:.edu, site:.org, site:.ac.uk and so on, or only certain newspaper sites, or books (e.g. G**gle Books), or journal articles (G**gle Scholar, & others). But even books and newspapers aren't always well edited; newspaper and media websites now often include unedited blog responses written by users; and these days, many if not most journal articles, especially in the sciences, are written by non-native speakers. Also, more and more, quality content on the internet is now available only on a fee or subscription basis, which means it may not even show up on an ordinary search. All those reasons are why it seems to me that the most reliable method is to compare usage guides written by people who specifically know and care about English style.
But it wouldn't surprise me if not many of them have discussed an issue like this in detail. I can imagine contexts in which any of MikeE's options in #10 would fit, and I don't think we can draw a conclusion about this particular sentence without knowing more about the writer's intent. That's likely to be true with other such sentences: the comma placement can change the emphasis, but either choice could make sense depending on what you want to express.
That said, I would probably go for one or no commas here, because I can't see any reason to set off 'more important' as an afterthought. As MikeE said, that would mean essentially 'other facts -- which, by the way, also happen to be more important.' But it seems to me that that would be logically contradictory; if the facts are indeed important, then the adjective 'important' is itself important, not optional or added in passing. Without it, the sentence wouldn't have the same meaning -- so to me, it shouldn't be set off parenthetically with two commas, which I agree disrupt the flow of the sentence.