Really poor defensive "analyst" here (so I put this out there to get educated), but don't we generally think that when a team is in nickel, the two remaining linebackers tend to have two somewhat different roles --- one of which emphasizes a lot of field area coverage (since we're worried about passing mainly), and yet we still need a number one thumper in case of an interior run "surprise"? ... and whereas Kiser is pretty good at both, he's perhaps number two at both? ... also, I got the (maybe wrong) impression, that Bertrand was considered by his teammates the lead killerdog LB and his "presence" was important?
Adding in a defense of Jack Kiser, if my DC designed defenses where I had a defined job and did it correctly in terms of my "fits" in the scheme, and the offense (not being suicidal or stupid) didn't often choose to run right into that correct fit, am I not doing my job just fine and affecting the game? A LOT of DLinemen do the exact same thing without many glory moments.
Lastly, I kind of get the "very good in college, not so much NFL" view of our guys, but would caution the negativism with what is often an ND characteristic (actually two): scheme-solid intelligence/film-learning and team-first character/effort. Those are valued by many NFL coaching staffs.