The signal I’ve started looking for is an above the fold “minutes to read” stat. Sites, like Medium, that have it are practically all worth ignoring because it’s either astroturfing or just navel gazing.
Absolutely agreed, there's a huge difference between a 5 minute article you can quickly read whenever you stumble upon it, and a 30 minute post (like acoup.blog's excellent articles) that you might have to save to read later.