First, I actually like the fact that Jake was "under-utilized" (though even I agree he should've shown up more in season seven). I liked that the writers seemed content to have him be a rather ordinary teenager/young adult rather than trying to find a way to shoehorn him into the action. He was there when they wanted to do a parent/child scene with Sisko (and like most people I think that whole relationship was portrayed well) and he had a few sub-plots over the years along the lines of "growing up on the station", "looking for a career", etc, but when he wasn't needed they didn't feel a need to use him "just because". I like that I can look at his role in the series and think "he was pretty normal, considering". So I don't see him as a waste of space, instead I'm pleased that he was an optional part of a story rather than a component they felt had to be used.
What we did get out of him, I liked. Maybe on his own he's not particularly interesting - but then, as I said, I appreciate the "normality" - but his role is pretty much to be Ben Sisko's child, and in that he was always a welcome part of the show. So I don't really see too much of a need to judge the character as much other than a supporting character for The Sisko.
That said, just as Sisko was interesing for being the only captain bringing a child with him, he probably would have been interesting as the only captain to have a spouse with him, too. Sisko's domestic life was a nice addition to Trek, and I guess having Jennifer along instead of Jake could've worked fine. I like to think they'd have got some good scenes out of that, but I'm happy with what we got.
