McGarigle the player was great. I have absolutely no doubts he can coach up the LB's based on how great he was.
Running a defense? Well, McGarigle played in a scheme run by the worst DC in all of Division I football for four years. If it were a cheese, it would be Swiss. Everytime I start thinking how bad McCall is, I remember how bad Colby was, and then I'm like, well, McCall isn't really that bad. That experience playing the scheme in itself, likely sets back McGarigle's DC development a few years through no fault of his own. Nothing some years learning under Hank and a dose of Vandy can't overcome. Of course, there may have been hard first hand lessons learned on what NOT to do, and what doesn't kill you makes you stronger, so there's that too.