I think you might have "I want KK to succeed" rose colored glasses on.
Staal makes the guys he plays with better. KK is being made to look better because of who he plays with. I'm not saying KK won't improve long term, but if an NHL coach were in a situation where you have to choose. Stastny-KK-Noesen vs. Martinook-Staal-Fast as the 3rd line, I confident 32 out of 32 coaches would pick Martinook-Staal-Fast based on how the players are performing today.
Other points.
1) It isn't our 5v5 letting us down in the playoffs. It's abysmal special teams, losing our starting goalie (last season), and other teams having superior goaltending.
2) I'm fine with giving Staal some time off and spreading the TOI around. That doesn't necessitate playing him on the 4th line for the rest of the season.