Your description of what the TCH steering feels like is identical to my thoughts. This is purely a gut feel, but I think the wheels on a properly aligned car want to go straight. They don't want to be at an angle to the direction you are going and a force is created to self straighten them.

I think as a result of the EPS there is too much stiction or drag, or not enough mechanical advantage to let it self straighten. Not the same, but kind of like a worm gear driving another gear. If the power comes from the worm, you easily drive the other gear. If the power comes from the gear you can't make the worm turn.

That said, some have reported an improvement from a wheel alignment. More toe in if I recall correctly. A range is given in the Toyota specs and I believe it was adjusted to the max toe in limit. Tire wear may increase as a result though...