Yeah the "more than a paragraph or two" is key here. Indicators of AI writing work both ways; the more text you write, the more likely you are to "slip" and use some phrasing or syntactical constructions uncommon in LLM output. (This is why AI detectors perform worse on shorter excerpts.)

I posted this elsewhere, but convincingly, consistently "writing like AI" and never slipping once takes an amount of knowledge and skill analogous to art forgery. Except that with art forgery you can at least make millions of dollars off it.