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.
I'm not so sure I buy your argument where TNG is concerned. LeVar Burton, going into TNG was the most popular actor for American audiences (due to Roots and Reading Rainbow). Geordi should've been a much bigger character in order to capitalize off his familiarity and relative popularity, but they didn't do much with his character. Ergo his character didn't become 'popular', which meant he got even less development. So I think the writers/powers that be, have some say in terms of who gets how much of the pie. And that in turn leads the audience. It doesn't always work, ex. Wesley, who I think was given some prominent screentime, that created a fan backlash, but I think it has worked more often than not. If the writers get a feel for a certain character I think they are more apt to write or find ways to do something with that character.
Geordi and Dr. Crusher didn't get that. Despite LaForge's popularity and the potential romantic tension existent in the Crusher-Picard relationship, that never really got the attention it deserved during the course of the series. Trek Lit. has handled it much better.
Regarding VOY, I'm not sure how much behind-the-scenes, office politics played a part in who got how much screentime and development. It certainly didn't hurt Jeri Ryan to be in a relationship with Brannon Braga during her time on the show, to be honest. Though I thought Ryan is a good actress and Seven was an interesting character until they decided to make the show mostly about her.
On the surface I thought VOY had a very nice looking, interesting cast, and I think the writing staff failed a good number of them. Even Janeway came off as an uneven character, though she did get development. The best were the Doctor and Seven. Torres, Paris, Neelix, and Tuvok all had interesting hooks about them as characters, that were sometimes explored, sometimes not. Even Chakotay and Kim got some episodes (like Mayweather), but I can accept how they and most of the cast except Doctor, Janeway, and Seven weren't sufficiently developed.