The problem with DS9 wasn't what it was. It was that it was serial as much as episodic, and there were problems with syndication competition with TNG until that show went off the air. I have a soft spot for Voyager, although I can critique the issues with it (which I won't do here for the most part). Voyager could have been more morally complicated, bridging a gap between the style of DS9 and TNG. I think a problem with it is if you wanted to do TNG part II, literally just do so. Keep it in known space as a different ship and different characters than the Enterprise. Exploring the galaxy after the Dominion War frankly would have been interesting in itself. New missions with the same formula, and with a changed galactic stage in the background. I think among the problems with both VOY and ENT was that they did not tailor it enough to the characters and setting. It felt all too often like it was a story that could have happened to any other show. And the other shows did not do that. For a terrible metaphor, it's like throwing a tarp named "Star Trek" over furniture. In TNG and DS9, it took the shape of the furniture underneath it. In VOY and ENT, it often didn't take the shape of anything it covered.