Well Yoda didn't really join the group, he just mentored the lead for a bit. And neither the Emperor or Fett was prominent. Fett just looked cool for a couple scenes and I think had two or three lines of dialogue, while the Emperor was just in one scene. He had about as much of a "presence" as he did in Star Wars.
And I hate to use the whole X-Men ensemble as an example, as some of those characters really got screen time at the expense of Cyclops.
But yes, it's possible to add a few more supporting characters