To which we can compare the astute-drafting Spurs, for whom over the last 20 years the following players have made it to their second contract:
Tony Parker
Tiago Splitter
Kawhi Leonard
Dejounte Murray
Derrick White
Manu Ginobili sort of (was drafted more than 20 years ago but came over less than 20 years ago)
So two of the players on there (and the sort-of) are better than the Kings' players (not like Cousins and Fox are slouches) but the count is the same. 5 (+1) have made it to the second contract.
Parker a 3x all-star, fringe-HoF, Manu is a Hof (if we're counting him in our list), Murray is well on his way to being a career all-star type, Kawhi is a HoF, Derrick White is a quality starting guard and Tiago Splitter, the worst guy on the list, was a quality rotational big for 5 years with the Spurs before falling off.
Not to mention, they probably have the worst draft capital to work with in the NBA the last 20 years because of how consistently dominant they've been, only recently falling off. I think they win.
But point well taken overall. My initial thought was the Kings have been especially bad at getting guys to second contracts, but perhaps that sort of "2nd contract hit rate" is somewhat standard. If you factor in busts and trades, most teams are probably in that 5-10 range. Perhaps our bigger problem is on rookie guys we did hit on, we let them walk for nothing without a plan.