If by "fix this" you mean we are trying to create a perennial contender here, like Seattle has done with having Russell Wilson, or GB has done with having Rogers, and the Chiefs are in the process of doing with Mahomes....then it needs to be blown up.
Completely new FO. That FO has to have a 2-3 year TEAM building plan that incorporates what we have in KM, and builds around his strengths, but is also building a culture that pieces can be replaced but expectations remain high. Arians was actually in the process of building that here..."next man up" was something that the team bought into. I fully believe that if we would have drafted Derek Carr to be Palmer's eventual replacement, BA would still be here and we would have at least a superbowl appearance...but that is a different topic.
Back to the new FO. You need to bring in a GM that nails picks in bringing in nfl starters...guys that would actually start on other NFL teams...and they need to get those types of guys in rounds 1-4 consistently, almost every year. No GM bats 1000, but you gotta get 3 guys out of every draft...no matter your draft positions that are contributing in the next 2-3 years and are getting a 2nd contract here.
I'm more old school, so I would love to see a GM build the trenches, but I know we have other needs.
It all has to start with the GM. Keim has not been a completely terrible GM...he has made some great trades, but his drafting has been bad...and his time has run it's course here. Its time to change the culture, and that means a fresh start.
I do not pretend to know who that magical GM is, but I hope Bidwill tells someone, "I want superbowl trophies in AZ", and then gets out of their way. Let the new GM choose the coaches and the new look players.