Date and the Doctor were very different, with very different issues
They were both artificial people trying to become more human and many of the Doctor's stories and issues were already explored on TNG with Data. Even Robert Picardo said that.
That said, in character and physiology they were very different, I agree. I didn't mind seeing those same issues explored with a very different character on VOY, especially since that character, imo, was one of the best ever in ST played by a great actor like Picardo.
Similarly, while B'lanna is somewhat similar to Spock in having a pedigree she wasn't happy about and to Worf with having a Klingon heritage, I thought she was significantly different from the two of them to be an interesting character in her own right.
Tuvok, though, I think he was a bit too similar to Spock, despite what some people have pointed out about him, i.e. his cynicism which was reflected in his choice of careers and his career-path in SF, not having a side of him that he was ashamed off, like Spock was. I still liked the character, and, truthfully, I'm not sure what else you could do to make him more different from Spock and whether that would've been a good thing, i.e. would I have liked that? I did like Tim Russ' Tuvok a lot and I wish they'd done a lot more with him.
Finally, Janeway's been said by both the writers and some fans to be more like Kirk than Picard. I don't know about that. In the sense she is more shoot from the hip and less staid than Picard and goes on the away teams, I"d say yes. However, I've also seen her being a stickler for principles sometimes, like Picard, and, at other times, it appears she throws them to the wind and even does stuff Kirk would never think of doing (i.e. wanting to execute one of the Equinox's crew and actively changing time for a few lives in Endgame). Maybe that's what Ron Moore was referring to when he said that Janeway's characterization appeared inconsistent. Whatever, I think, in the end, that Janeway wasn't like Picard or Kirk, which was a good thing for VOY. I think the writers could've done a better job defining her character, but Kate Mulgrew luckily was such a good actress that she won me over despite sometimes having weak writing for her character. I think she was very well cast as Janeway.
Life is crazy most of the time, but I'm getting there 
It's all a cunning plan 
, but I also have a soft spot for Vulcans, so Tuvok gets my number 2 sslot.
