Real people change over time but not in the direction you're allowed to change on TV.
Real people start with one group of idiosyncracies, strengths and weaknesses, and then later they have a totally different group of idiosyncracies, strengths and weaknesses.
TV characters start with one group of idiosyncracies and weaknesses then gradually blunt them over time without adding new ones. Long TV series' character development is just a slow gravity of every character's personality quirks toward the center, and no Star Trek is any exception.
I liked TNG and Voyager. TNG has a better group of actors and better writing, but Voy has a good cast with good chemistry and at least half the episodes are well written. I definitely end up coming back to TNG and DS9 more often than Voyager, but that's like comparing a good beer to a great one. Voyager is Sam Adams Boston Lager and TNG and DS9 are the fancy craft beers that come corked.