I disagree. I think BB hasn't been able to find someone who fits this bill (probably since Phifer retired) but not for lack of looking. I think Jamie Collins was this guy; I think they've tried to find this guy multiple times since.They are running four deep at LB with Hightower, Van Noy, Bentley, and Roberts. You could argue for putting it in the second category given Van Noy, Roberts, and Hightower are nearing the end of their contracts, but I don't see it up with the more urgent needs you have listed there.
I know there's some clamor for 230-pound coverage LBs, but Belichick hasn't compromised on this to date and I don't see him doing so after they won a SB largely on their 250-pound LBs just mauling an undersized Rams team. I think if anything they'd address this via safety (if they had a second Chung, he would play a lot).
If Gurley had been the pre-injury Gurley, if Hunt hadn't been suspended, I think this hole would have been far more glaring.
Finding this guy is really hard -- it's why TB12 and JMcD salivate whenever they see most LB's lined up opposite White, Burkhead, Edelman, or Gronk. And I think it's a big part of why the RPO gives the Pats such fits.