Sorry for pulling Harry Potter into this but I can't help quoting here a statement by Arthur Weasely...

Never trust anything that can think for itself.

AI cannot "think" of course but the effect is the same - it simulates a human brain. Sometimes, it gives great results but mostly it's faulty and very robotic (I mean what else can you expect from a bot).

I think your assumptions about false positive results are somewhat correct. I haven't experimented enough to give further opinion on this.

Personally, I use a similar approach to yours for languages that I don't know. But for English and Urdu, I generally don't use any AI-detector. Sometimes, it's the robotic tone that gives away and sometimes it's simply the author's writing style, which in some cases I'm already familiar with, so I know when it doesn't sound like him/her.

We all need to be more open and flexible in quality control. I don't deny the kinds of scams we are facing on steem but that doesn't mean we should shut our brains and catch AI authors solely with AI detectors.