I don't think this is entirely true. Getting in the habit of writing, even if a lot of it is things other people have said better, means that when you do have something novel to say you will be much more practiced.
My experience is that when people try to only write the good posts they don't end up publishing things, but if they write hundreds of posts dozens will be good.
I agree, and you’re actually supporting my argument with additional reasons against OP haha.
But in the case of a research blog about a new research paper I think my point above trends closer to true, as the novelty of the subject guarantees novelty of the blog.
My experience is that when people try to only write the good posts they don't end up publishing things, but if they write hundreds of posts dozens will be good.