Plus, so many scenes and eps with Seven were directly about her interactions with Janeway. More scenes for Jeri usually meant more scenes for Kate, so what's the big deal?
I am not particularly a big fan of Mulgrew, Beltran or Ryan. I draw a line between the actor and the character. I love Voyager's characters, not so much the actors.
That being said, the situation that placed Ryan in the series in season three, had to be at the very least awkward. That situation has always reminded me of the movie, "All About Eve." You only have Ryan's word that she was treated badly, and Mulgrew's silence. I do know if I was hired to be the star of a television series and then had someone added in the middle to "save" the show, I'd be pretty pissed too. Then soon that "new star" latches on to one of the producers, I'd be suspicious as hell and would hold that person at a definite arm's length at the very least.