It's not just a matter of imagination or creativity. Dragon Ball isn't a series with a flexible format to begin with, and it also relies a lot on the nostalgia from long time fans. The way things are right now only Goku and Vegeta going away, even if temporarily, would allow those two to have proper development, since there's very little space otherwise (especially with the fusion gimmick always being present). Even a 'tag along' adventure in which they get new powers wouldn't shift the focus from Goku and Vegeta which would end up getting the bigger portion of the pie.
I agree that they should be handled better but IMO I don't ever see the writers making them justice at the level that their fandom fans want, not until we go beyond EoZ at the very least.