When I think of rationalist blog posts, I think LessWrong and ACX. There is probably more to know. Across 46,000 posts on LW the average word length is 1,300 words as of May 2026. That doesn't seem too bad.
Regarding the varying degree of quality I wanted to note that this is a public forum where anyone is allowed to create an account and post public articles. Anyone is allowed to call themselves a "rationalist" if they want to. I wonder if most who read articles there and post occasionally do label themselves though. I know some who don't.