Whereas most scientific bloggers post things they are interested in and therefore feel have something to say.
You have a point but from all scientists I know myself there's not one for which this applies. Might depend on the field though and I'm not denying there's a bunch of impossible-to-reproduce-crap published and there are rotten apples everywhere. But what I see (in fundamental research which is usually not as publicly known as other kinds) doesn't come near what you describe, even though it's anecdotal of course.. Yes there is pressure to publish but their papers aren't 'scinetific-looking', they're properly scientific and they are just the length needed to describe the findings on the subject. And there is an abundance of motivation for reviewing mostly inspired by wanting to make sure everything is as correct as possible, for the sake of research.
These grants are aimed at building a working technology and strengthening national economy, so there's nothing wrong with the approach per se, but when your reviewers share your values they have little motivation to find every possible mistake in your paper, at least for second- or third-rate journals (which are still indexed in WoS so are perfectly enough for the funding agency).
Good networks concentrate intelligence by providing feedback and support that helps the network converge on useful, original insight.
Bad/malicious networks destroy it with noise and false information, creating a feedback network that suppresses reality-based original insight.
The process of blogging is irrelevant. So is the process of peer review.
It's the quality of the networks around each area of interest that defines the real value, not the process.
E.g. peer review works well when it's part of a high quality network. When it isn't, it's no better than random posting.
Free and gated idea exchange create completely different communities, with completely different problems and advantages.
I think is they key point here which the OP seems to ignore completely: I sort of agree with everything the OP states, but he also forgets some key aspects on blogging. For instance anyone can post whatever even on subjects he/she really doesn't know a lot about. Also, not every blog post does get reviews from all sides and might only get 'yes good' replies originating solely from confirmation bias while the lack of any criticism doesn't make everything right but for instance just indicates the critics didn't find their way to the blog post.