Some more thought should go into this assumption. It's possible that an R&R will increase stress on the frame. On the road, when your bike swings when you are out of the saddle, you are still applying mostly downward force into the pedals and countering with upwards force on the bars, so there is some frame twist. Also, in the saddle, gravity is only applying downward force to the saddle, on-axis.

On an R&R, when you are in the saddle, it's possible for you to lean over. Now you have sideloads going into your saddle that you will never see on the road as the R&R fights to keep you upright. Since it allows the swing, you can get much further off center on an R&R than a Road Machine.

Of course, that doesn't mean anything bad will happen. I haven't heard of anyone damaging a frame in a trainer, ever. This is not a significant problem.