User blog comment:Xilinoc/Ch. 562 - THE VILLAIN 2 (Mask De Masculine is a Mexican luchador in a German army)/@comment-24297669-20131217215754/@comment-11051098-20131218214830

It annoys me that Kensei and Rose lost so easily in the first place, despite using Bankai. But as it's explained further up in the comments, it might be the fact that they probably didn't do much fighting during the century they spent in the world of the living, and the fighting and training they've done after they became captains again, have only been for 1,5 years.

Next to that, Kensei was caught off-guard by Mask's increased power after James cheered him on, even though I don't see how he could be that easily dominated. And Rose screwed up when he explained how his Bankai works, and was caught off-guard when Mask crushed his eardrums to negate it.

I do think Renji seems too powerful compared to the last time, but he was caught by surprise then. Mask showed up all in a sudden, grabbed Zabimaru and punched Renji across half of Seireitei before he could react. I suppose Kirio's food, the intense reiryoku around Ichibei's palace and the training Renji got there, are the reasons for his new increased strength.