Looking more deeply at his numbers, I might have to agree with you.
He's been incredibly young, so it's different comparing him to past guys from the NBP. He's got a career 859 OPS over there and he's been a stud the past two years, with a nearly 1000 OPS at 21 and 22 y/o, albeit only in about 600 PA total. Nori Aoki, for example, was a career 857 OPS with multiple seasons in the mid 900s. Fukudome was 889 and was around 1000 for a 6-year period before coming over. Iwamura was 850ish. Kaz Matsui was about 800 inclding some young years in the 900s. None of those guys put up the numbers Otani has at ages 21 and 22, though, they almost all were in their mid-20s before reaching those numbers.
Hideki Matsui may be the best comp for the bat, and obviously he had the best MLB career anyone from Japan has had at the plate. He had nearly a 1000 OPS for his career in Japan, and got to that level by his Age 22 season.