I was also rather late to the party here. I first watched the game at a family event, and was rather distracted by the JG trade so did not do my normal re-watching. Your thoughts on Roberts reminded me of something:
I agree with luuked's more general point. But I don't think shooting the gap is
necessarily a negative in our defense. It might just limit which defensive calls are used.
This Grantland article describes how our defense is truly a 4-3 & 3-4 hybrid. At times one side of the DL is one-gapping, where the other two-gapping. AFAIK, in traditional 4-3 run fits, shooting the gap as a LB is ok. You are only responsible for that one gap, so forcing the RB to go to a different hole is good. In traditional 3-4 defense, you don't want your ILBs shooting gaps as much. This whole thing might be an oversimplification, but I believe it is generally true.
In Mayo's 11/7/17 QS podcast, he describes situations where shooting a gap is intended. He briefly describes a "dolphin" defensive call, where 3-tech DL (lined up outside guard) shoot the gaps between guard & tackle. Unfortunately, Mayo is interrupted too much to fully explain that defensive call. He also describes a "ball & chain" theme where Spikes would aggressively attack the running play to create disruption, freeing up Mayo to make the tackle (this might not actually be shooting a gap, would love input on this).
Going back to Roberts: First, I assume BB & co. know which calls maximize Robert's strengths. I also assume BB is trying to develop his versatility, so might ask him to try other techniques from time to time.