Check Airman
No question that using available competent resources is good. The real quest is whether the jump seater was a critical resource. Would the captain and FO alone been able to handle the non normal situation successfully? I realize professional pilots are reluctant to admit they could not. But there are some examples to the contrary.
The issue though is not pilot competence, but aircraft design and whether it is good enough, safe enough for two pilots to handle the potential nonnormals.