The UFC is more of a sink or swim league. You won't get fighters up to 17-0 IN the UFC. They may get that on the regional scene BEFORE the UFC, but not in the UFC itself. And there's nothing wrong with Bellator's model of developing prospects from fight 1, it's just a different strategy, many fighters were picked up by strikeforce/bellator and started from earlier in their careers and went on to be great UFC fighters even champions.
You have to remember that the numbers as far as records go really do not matter. The UFC will sign guys at 5-0, and sign guys at 25-0, those guys aren't necessarily differently able or differently talented, one has just had less record amelioration. The 0 also really doesn't matter that much, particularly if someone lost a fight early in their career because they got caught by something when they were new to the sport. Someone like Khusein Askhabov, I'm a big fan of him actually, but it's not meaningful to pretend he's better than say Cory Sandhagen because Sandhagen has the 14-3 and Khusein is 23-0. In the case of AJ McKee, he has a lot of wins over solid regional guys, guys who are probably UFC entry level, guys akin to contender series winners or the regional guys who get signed for local cards, maybe even some fading seasoned vets. How many guys has he beaten who are say top 20 in the division in the world? Maybe one, Caldwell but maybe not even because Caldwell is typically 135. So if you compare him to a guy like Ilia Topuria, he has 6 more wins, I'd say their records are about equally impressive.