I would have agreed with you a month+ back - since I only saw one side - the AI.
However, I've been playing now with Kerby on my team for 2 months solid. (even without him being traited).
He has fired off 496 times ( i have been keeping track) and has successfully devoured 267 times
Now I can take a snap shot out of there and show skewered stats
there is a 75 attempt run where he did 100%
there is a 30 attempt run where he did 0% I chocked it up to him eating the mech bombots
I don't cast devour in every battle but I did use him a lot