I don't see what Katie has done to think that, i honestly haven't laughed at anything she's done... not even one thing. Even Patsy and Keith have engaged me in such a way... nor have i found anything about her interesting in a positive way, not even once throughout the season.
If anything i feel like the season is worse off with her there.
Perez, i have found him funny and entertaining at times but i could live with him going on the chance that within the group dynamic it lightens things up a bit in there and it's not so gloomy and dark. I don't feel he's completely responsible for it all but the majority of the group has accepted that perspective and no matter what i think if Perez were to be removed from the equation it could have that change occur.
What i question about that scenario, however... is it could possibly shift in the other direction and put more pressure on Nadia/Alicia which is one of the worst case scenarios for me. Katie would have to leave before Perez left to better the chance that doesn't happen for me to embrace that scenario.
Ideally, if both Perez/Katie could stay in there and it could become a more pleasant group which would require big change from both of them... that would be good but there's a better chance that i'll become Katie's number 1 fan than that happening, and that isn't going to happen.