I believe it is more route dependent than operator dependent.

I tried for months this year to get a KIX-ISG (on JAC) reward, but nothing ever available (or maybe not offered?). In the end, I had to stump up the cash for my flight in September.

I have been successful in getting a HND-KIX flight on Avios that was operated by JAL Express.

That being said, Avios availability for domestic Japanese flights is not great in my experience.