User blog comment:Xilinoc/Ch. 576 - THE KILLERS HIGH 2/@comment-31283382-20140410044535/@comment-11051098-20140410214533

I disagree. He was overpowered by his opponent, which likely caused Gremmy to lose his faith in him and see no point in letting him live. But being created by Gremmy, Guenael was only as strong as Gremmy made him.

At the very least, he was only partially responsible for his death due to Yachiru's Shikai.