I disagree. I think the defense underperformed relative to talent under Williams. You cannot call losing a rotational DE (Sims) and a slightly above average 4-3 DE (Hayes) a "rebuild." A defensive line of Donald-Brockers-Easley can and should be great.
Tru is another matter completely, and ties in with Donald and Ogletree and has to do with contracts and not fit or talent. There is a good case for both sides as to why Tru will not sign (Tru wants to test free agency and have choice or else sign a woefully inflated contract to stay and the Rams don't like either of those options and choose the lesser of three evils in franchising), so if you have to trade him, it is not as a rebuild, but simply under forced circumstances.
The entire secondary needs to be rebuilt, anyway. Tru is a problem (good, but not great, but will be paid as super great by someone), Joyner will be a free agent next year, we are still uncertain about Gaines, McDonald is gone (and only average, anyway) and we have zero depth.
Last year was the year to complain about rebuilding when they couldn't lock up everybody long term. Just my opinion.