However, it is not optimal for finishing off unbreakable immunes. A GT/GPA base would be better than a CA. Also, Guillaume's + CoH is better most of the times: the extra CB will be better than 300%ed vs high hp foes, and it is rare that 300%ed will require 1 less jab to finish off a low hp monster.
This is especially the case when he already has quite some off-weapon ED (e.g. Might aura).
In any case, do not switch to defensive setups if your merc is not dying.