You’re still ignoring the fact that it wasn’t explained in ROTJ as to why she wasn’t in STAR WARS or ESB. So why should another film have to pick up the slack because the OT had so so writing in that department?
It’s a very simple explanation – Mon Mothma has assumed the leadership role of the Rebel Alliance sometime between TESB and ROTJ.
We see her found the early seeds for the Rebellion with Bail Organa and Padme in ROTS, which needless to say is part of Disney’s canon even if many of us here don’t like to acknowledge it.
They even used the same actress in Rogue One.