IMO, one thing that the article missed on was comparing of stats among the pitchers. They only used their last year in NPB, instead of an average of the last 3 years. IMO, the last 3 years is a more accurate comparison because players can have a fluke year. See RA Dickey.
If you look at the last 3 years of Diaske, Darvish, and Tanaka. Left out Kuroda and Iwakuma because we all know they didn't come to the US as highly touted as those three.
Diaske
547.1 IP, 437 HIts, 125 BB, 146 ER, 44 HR, 553 K
1.027 WHIP, 2.40 ERA, 0.72 HR/9, 9.09 K/9
Darvish
616 IP, 432 Hits, 128 BB, 112 ER, 19 HR, 665 K
0.909 WHIP, 1.63 ERA, 0.27 HR/9, 9.71 K/9
Tanaka
614.1 IP, 499 Hits, 78 BB, 98 ER, 18 HR, 593 K
0.939 WHIP, 1.43 ERA, 0.26 HR/9, 8.69 K/9
So definitely had better stats than Matsuzaka. But the WHIP and the K isn't there with Darvish. Which is concerning since Darvish hasn't had great control at the MLB level.