I hear you around scheming around linebackers and I agree with you that you can play 2 LBs most of the time. However, it is a position where guys get hurt a lot and, while Jamin has stayed healthy, the other starters we have had over the years have missed time, whether it be Holcomb, Bostic or KPL. They barely got by last year with Jamin staying healthy but if both guys were to go down, they are in serious trouble. They had a bunch of issues but the LB injuries the Browns had last year were the primary reason their D was terrible. There is only so much masking you could do if you are forced to start Mayo and Hudson.
On OL, there are different theories around it. I think it is Logan Paulsen whose philosophy is that you don't need studs but you need at least a legitimate starter at each spot so you don't have a weak link. I think they should sign Jason Peters or Dalton Risner for additional insurance at LG but I don't feel very worried about any other spot on the OL.