I would, respectfully, disagree a little bit. True, in both cases the wives have sex with other people. With Stags it is done in a consenting and mutually enjoyable manner. And the Stag and wife continue to have a great sex life together.
For cucks, at hugely varying levels, the wife makes all the decisions on who and when she’ll be with others and might forse the cuck to be included in humiliating ways. And she may cut out off any sex life with her husband altogether.
the two sides are really very unique.