I'm thinking of lowering the standards for what can be included as AI-assisted because both writer.com and writefull.com are extremely lenient compared to hivemoderation.com.
...
I didn't try writefull.com very often, but it says that it tries to find only ChatGPT written texts. Maybe the problem is in that.
writer.com gives false negative results really often. I don't know why do many use this detector.
Try
https://copyleaks.com/ai-content-detector. It gives false negative results too and who probably stole the nlovric's acc would also pass it's check with about just 30+% of AI probability. But comparing to other tools I'd say it works good and I haven't ever seen it giving false positive results yet.