Claiming that Japanese players experience a rather significant drop-off in power when they come over to America is not "speaking as if I have insider information."
Player - SLG in Japan - SLG in America
Ichiro Suzki - .522 - .430
Hideki Matsui - .582 - .478
Akinori Iwamura - .519 - .394
Kazuo Matsui - .486 - .395
Kosuke Fukudome - .543 - .379
Kenji Johjima - .517 - .412
Tadahito Iguchi - .471 - .401
Tsuyoshi Shinjo - .432 - .370
So Taguchi - .387 - .385
That's 9 players, all but one of whom experienced massive dropoffs in power upon arrival in America, and the one that didn't was a guy without much power in Japan.
It's not "insider information" that the level of competition in Japan is lower than that of the MLB. It's accepted fact.