RB is stable and versatile. They aren't paying for a backup linebacker with all their sub packages, so get used to the STers and PS players.
I agree with almost all that you posted, so let me focus on where I disagree.
RUNNING BACK
I don't like our situation. Ridley is indeed solid. Vereen is often injured, but a fine asset. Bolden is valuable as a special teamer, but not good for much else. White seems a good enough prospect for the future. IMHO, we one player light. I would have preferred an veteran addition or a upgrade to Bolden.
Let's be blunt (or Blount). If Ridley were injured, we'd be screwed.
LINEBACKER
No we aren't paying a #4 or #5 linebacker. Last year, we had Fletcher and Collins. This year we have whoever PS player is activated, Fleming in week one, Skinner this week. IMHO, it would be better to have one real backup.
ROSTER CHANGES - BOTTOM LINE
I don't expect us to do anything at RB or TE unless there is an injury. I could see us continuing to have transactions at LB, S and ST all year. So, for me, Belichick has chosen to live with the lack of depth at RB and LB. And yes, Belichick will continue to try out players. We need players for the Practice Squad, the speed dial list, for the future, and in case of injury.
For this week, I could see us activating Davis, or not.