So what does Favors do extraordinarily better than Davis? Let us see here....
Rebounds - surely not, Davis averages 11.4 boards per36 for his career. Exceptional rebounder.
Blocks - nope about the same rate.
Passing - nope same assist rate.
Mid range shooting 10-16' - nope Davis was 44% to Favors 40% surprise, surprise, surprise. He could make up most of Favors points advantage if he got more shots.
Favors has a higher PER, but Davis has a higher RPM (1.03 to .53).
I'll give Favors the edge on overall team defense, but Davis is not a slouch.
So ya, it was an overpay, there is no freakin way Favors is over 4x better than Ed Davis. There is no stat to remotely prove it.