Show me the poll that people voted Voyager the best series. Everybody I've ever talked to except maybe 10% of the people on this board cite either TOS, TNG or DS9 as their favorite. And the younger people I talk to who never watched Star Trek when it was airing tend to heavily favor DS9.
Seven was a good addition to the show, but Kes was also a bad subtraction. Like I said, she had the least sexy gimmick so she was the hardest to write for, and those writers had a lazy streak. They would have had to try harder to find good stories for Kes, certainly. But the stories they could have come up with if they made the effort were far more original than Seven's stories, because there weren't the obvious genre precedents for her that there were for Seven.
Yes, Voyager did always get good enough ratings to stay on the air. At the time a 3.0 was UPN's highest rated show. But it was also far more accessible than DS9 and it's where all the marketing resources went to and it was still consistently lower rated than DS9. And, I'm a fan of Voyager, but it seems every time the subject of Voyager comes up outside of this board it's in the context of me having to defend it.