My feeling is that something fundamentally wrong and I would bet on something like this going on.
You may find this article worth reading:
Boeing 787 Dreamliner Rolls Out Smoother Ride with Gust Suppression - 2007-06-04 00:00:00 - Design News
The information these (pre-787) dampers work on is from sensors of the inertial response. There has to be movement to damp. The movement is complex, and the airplane is large and flexible, and there are only a few control surfaces to effect damping with. No chance of a perfect result, at least not for all observers, some a hundred feet from the CG. Even if you act
before the plane starts to move, as the 787 intends to, you still can't quiet all those motions. This is why the article mentions a focus on modes that annoy or cause illness, as opposed to those most of us find pleasant. I believe this focus isn't new, and though you may find the 777 folks didn't get it quite right, I do believe it goes beyond "yaw damping" into "ride control".
Going back a whole step, it might be said that the reason that these unpleasant motions exist is that stability carries an aerodynamic penalty, and this incentivizes engineers to replace it with sensors and dampers and all sorts of annoying math. See, for example:
Method and apparatus for reducing ... - Google Patents
Unfortunately I've never had the privilege of riding in the back (or anywhere) in something like a stretched DC-8....did the early airliners have a more pleasant ride?