User blog comment:Eduardovongola/Renji Overpower/@comment-3219912-20131229073231

It boils down to this: 1. Kensei was taken off guard from James contributing to Mask's Superstar. Kensei would have ended him if not for that. 2. Rose was surprised by Mask crushing his eardrums after he explained his ability. If he didn't explain his bankai, he might have won. 3. Renji was trained by the Royal Guard, who are stronger than Gotei 13. He came into the battle knowing exactly what to do.

I feel people are forgetting that Hikifune said eating the special reiatsu enhanced food at her palace put Ichigo and Renji at a different level of power.