I disagree with the original poster that many characters on Voyager were underdeveloped.
Kim. He started out green and would do anything to get back to Earth. Paris' sidekick, second guesses himself whenever possible. Throughout Voyager's journey, Kim showed again and again that he is extremely capable engineer, he even designed the Astrometrics. And don't forget about Kim's speech in Endgame.
Kim is not a well developed character I agree but at least he isn't one dimension in the end like Chakotay. Chuckles is the only character I agree that is mostly stagnant in character development to the level of Mayweather.
But in an ensemble cast the less popular characters/actors must take a back seat. Even in TNG and DS9 had them.
TNG: Crusher and LaForge. Except for Crusher trying at command in the later seasons, what has changed for her character since season 1? Same with LaForge. After he's promoted to Chief Engineer, what other developments did he have? He's still just as lame with women as the beginning.
DS9: Jake and Jadzia. Besides being there to support Ben and refused to join StarFleet, what exactly made him a well developed character besides the obligatory teen turned to man cliche. Jadzia was Jadzia through and through. Even Ezri got more in one season than Jadzia in six.
Voyager/ENT was no different. Popular characters got more, less popular characters take the back seats.