When I use gravity stub cantilever to model a cantilever beam (Moment Connection at one end, Pin connection at the other end), I found it work like a pure cantilever after beam analysis.
The only way I found is to use a lateral beam with certain fixity to model a cantilever beam. But it's inconvenient to see the results in frame analysis.
Is there something undesirable about the "pure cantilever" treatment of the gravity stub cantilever beam? Surely that is what most users would want out of gravity-only beam analysis in RAM Steel.
When you make the beam (and the supporting column) lateral members, then finite element analysis is used within Ram Frame to determine the behavior, and that's when the rotation of the column becomes a factor in the cantilever deflection for example. Thus, my personal preference is to use gravity members for short cantilevers or brackets that support only other gravity beams, and use lateral members for longer beams that might be deflection critical, or where the fixity of the beam-column joint is important to the overall lateral resistance.