Yeah, I definitely agree that DS9 had the most character development of all the trek series. And maybe VOY does suffer from the TNG syndrome to some extent. But I can't really see how B'Elanna and Seven can be compared to Beverly and Deanna.
I'm not sure I can agree with that description. Seven and B'Elanna has a TON of character development compared to either Beverly or Deanna. (And no, eating chocolate doesn't count as character development). Saying that the VOY Women are depicted according to a TNG style type writing approach is seriously flawed.
Seven of Nine was essentially Picard.
Seven of Nine had only two and a half episodes of her being a Borg drone. Picard was a drone for two and a half episodes as well (Best of Both Worlds and Emissary). The majority of Seven's character had learned and grown just as much as any major character on TNG (Check below for an explanation on the TNG/VOY female comparisons).
That's quite an oversimplification to say the least. Aside from the fact that Seven isn't in any way, shape of form similar to Picard, neither in terms of backstory nor in personalty, the borg storyline didn't have any real impact of Picard's character arc aside from the episode "Family" (and later also in First Contact, but it's the television series we're discussing here, not the movies).
On the other hand, Seven being a partial borg/ex-drone had an impact on the majority of her story lines, from her dealing with her childhood and the assimilation of her parents in "The Raven", to her being unconfortable and distanceing herself from the crew, to her taking social lessons from the Doctor, to her interactions with the borg queen in several episodes, to her expertise being used in dealing with the borg on numerous occations, to her nanoprobes being used for various purposes (yeah, I know, the nanoprobes were overused as a plot device, but it still counts), to her interactions with Icheb and taking on responsibility of the Borg kids, to Seven being an integral part of the Unimatrix Zero storyline, to the episode when the Doctor is downloaded into Seven's borg implants and takes over her body, etc etc.
Finally, if we compare Seven from early S4 to S5 to late S7, there's a huge difference. At first, she's rather cold and detached, then later gradually opens up, befriends her crewmates and explores what it means to be an individal. In S4 and 5, she can be seen as rather childlike, which is also how the crew threats her at times (especially Janeway and the Doctor), but later she matures into a woman with adult responsibilities and relationships (taking care of the borg kids, mentoring Icheb, romancing with Chakotay etc). Seven gaining her humanity and integrating with the crew is a process that takes a long time.
Now, Deep Space Nine was different. By the fourth season they started to build on the characters from that point on. Character development was integrated into significant arcs.
Seven goes from being a borg drone, to being to an ex-borg dealing with her borg nature and struggling to integrate with the crew, who eventually faces her troubled memories both as a borg and as a human and learns a lot in the process, and then blossoms into a vulnerable yet strongwilled woman who's theme of reclaiming her humanity is an ongoing struggle for several seasons.
And B'Elanna goes from being an angry klingon woman belonging to a terrorist organization, to becoming an angry klingon woman who is an essential but uncomfortable part of the crew, who is restisting and pusing back every step of the way but eventually gives in and tries to learn how to control her volatile klingon nature with the help of Tuvok. Later, she enters a relationship with Tom, that eventually turns serious, with a lot of bumps along the ride. A relationship that is developed over 4 seasons (but initiated by events taking place in season 3), and she eventually marries him in early season 7 and than later gets pregnant. Each one of these story lines is a major character/story arc that changing the very fundamentals of her existance: Becoming an uncomfortable member of the Voyager crew; learning to integrate with her shipmates; dealing with her klingon nature; facing her troubled childhood; getting together with Tom; working out their relationship issues over several seasons; eventually marrying him; becoming pregnant; and finally delivering in late S7. Hell, this is a lot more character development than any of the male Voyager characters recieves (with the possible exception of the doctor).
In what way is this a typical TNG style depiction of women?
Picard and Crusher had a history. They might have not have went full throttle with it, but they did grow closer to one another.
Riker and Troi also had a history. They went on and off for a while, and Troi even dated Worf for a while; however, in the end: Riker and Troi ended back together with one another.
Yeah, but aside from the first couple of episodes, their history doesn't really show much. TNG was pretty worthless when it comes to long-term relationships. Picard/Chrusher is revived in the later seasons for a single episode, and then never heard of again. Picard has a new love interest in each TNG movie. And all references to the Riker/Troi romance on memory alpha (aside from Insurrection and Nemesis) are from the first five episodes. (Yeah I know, I'm really lousy, I actually had to check). Troi at one time also begins romancing with a transporter clone of Riker, but since Thomas Riker is not Will, that hardly counts.
Now, I have to admit I had nearly forgot about the Troi/Worf relationship which lasts for about half a season, since it's just seen in 2-3 episodes. I always remember those two as breaking up after a couple of episodes. Maybe if they had done something more with the Troi/Worf romance and actually developed it thoughout S/7 I could see it as something more than a one-off thing. When I saw them together in AGT I was at first

, then I was thinking "Oh yeah... those two". If a relationship is just seen in 2-3 episodes, then it's pretty hard to take it seriously. Maybe that's what you mean by TNG type storytelling (which at least B'Elanna/Tom can't be blamed for).
Finally, the TNG movies can't be used as an example of storytelling on the TNG television show.
And if you want to weigh in all of the scales: Janeway literally had no character development. She pretty much remained constant through the entire series. Granted, she had her odd mood swings, but that is the way she had always been.
Yeah, Janeway didn't get much character development, you've got a point there. Although she did get her fair share of story material. In terms of screen time and dialogue lines, Janeway far outshines all other Voyager characters. And together with Seven and B'Elanna, it's safe to say that Voyager is pretty balanced in how much screen time male and female characters get. TNG had both few female characters AND little screen time devoted to each female character. DS9 does have a couple of good female characters, but with an overwhelming cast of strong male characters they can't recieve as much attention as one would hope. For every Kira on DS9, there was an Odo, a Quark and Bashir. For Every Dax, there was a Sisko, Miles Obrien, Jake, Rom and Nog. For every Kai Winn there was a Dukat and Weyon.
On TNG, the only person with any major long-term character development and lasting character arcs is Worf. His klingon story arcs as well as his relationship with Keylahr and taking care of Alexander, are long-term stories that makes him reevalue his existence and grow. He finally comes to terms with his being klingon, and just as he is being accepted into the klingon culture, he has to take on the dishonor to save Q'onos from a civil war. That and taking care of Alexander are all inportant lessons that causes Worf to grow in meaningful ways.
Data also changes and grows throughout the show (just compare S1 Data with S7 Data), though it's less tangible than Worf. Unfortunately, too many of Data's lessons are things he has already forgotten about in the next episode. (Something which, at times, also Seven can be guilty of). And the emotion ship is never really used until the movies.
The rest of the TNG characters all have pretty much the same status in S7 as they do in the first seasons - and this on a federation starship in the alpha quadrant. Riker not getting his own ship after BoBW was in my opinion a huge cop-out by the writers/producers. Not following through with either Picard/Chrusher or Troi/Riker was another.
Voyager may not be DS9 in terms of character development, but at least they don't treat their female characters like TNG treats Chrusher and Troi (hell, Deanna almost gets more cahracter development on Voyager than she gets on TNG

).
But in Voyager's favor, it does have 3 powerful female characters who together gets at least as much screen time as their male counterparts, and even recieves more character development (not that underdeveloped male characters is anything to applaud).