In the afterword of the last Potions volume, he said that it was his 82nd. published work (including manga and spinoffs) and the 41st novel since he started writing 9 years ago. On average, he would finish a novel every two and a half months and was very proud of not having missed a single deadline.

That's an incredible track record, but in all fairness, all his works are basically the same, so it's more diligence than a wellspring of creativity that's the driving force here. I'm always joking that if you like one FUNA series, you like them all, which I personally see as a good thing. The flipside is true as well, though.