IMO, Staal isn't over-slotted. He's a perfectly fine 3C. The problem is we don't have a good 2C since Trochek left. I'm not against playing KK there instead of Drury, I just don't think either of them are good enough in that role so I'm kind of ambivalent to which one plays there.
Secondly, I don't agree that in an "ideal world KK would be perfect playing Staal's role". KK isn't anywhere near Staal in terms of defensive ability. Staal has been one of the best shut down centers in the NHL for years, and was better in that role as a 19 year old than KK or Drury is today. KK has never faced tough competition like Staal has either.
Could he become good enough to play that role? Maybe, but he hasn't demonstrated that yet. If Staal was gone and KK was our 3C, then I suspect that 3rd line won't be the same sort of "shut down" line that it is today, but it may provide more offense.