Voyager was in Borg space. So having Seven of Nine join the crew worked so much better. Her history as a Borg and her journey to recovery of her humanity was far more interesting than watching Kes handing hypos to the The Doctor, and setting Tuvok on fire (tho' I have to admit, that was pretty cool).
7's story is my favorite Trek tale so I agree with you. I was also bored by the super powered ingenue.