I would have loved if the film had a small Endgame moment with many familiar faces coming back from retirement for the ultimate battle. They wouldn’t even need to be named characters, but showing like, a Mon calamari bridge, or at least close-ups of the ships involved, would have sold the moment better.
Admiral Raddus would be a good Mon Calamari character to add, you could adjust his skin colour to make it look like a different older Mon Calamari.