Kickers aren't consistent from year to year. That's just math, and you can view the evidence in the chart in this link. Since kickers aren't consistent from year to year, it's almost impossible for a kicker to live up to a long-term contract that pays above the league average. So now we're locked into a four year contract that will probably only be worth it for two of those years, and the Panthers current cap situation is a case study for how those deals can screw teams over.
Kasay wasn't consistent for the 15 or so years he was a panther?