Do PF's need to be able to shoot outside of 10 ft? No, not really. Look at Blake Griffin's shot chart:
https://stats.nba.com/playerShotchart.html?PlayerID=201933
As a PF, you don't need to be able to hit a jump shot. Your job is to attack. Also, Blake Griffin doesn't do most of his damage in a post up style offense. He does his damage by facing his defender and attacking, much the same way Gordon does.
That is why having him play as a SF really drops his stock. His athleticism, while great is completely negated if he can't shoot. Drop off him 10 ft (ala what people would do to Brewer) and give him the jumpshot. He can't drive anymore. I don't care how athletic you are, if you aren't a threat to hit an outside shot, you aren't a threat to do much.
That is also why if he can play PF, his stock jumps through the roof. Now, you don't need to be able to hit an outside shot. Put him in the post, get the ball to him, let him face up with his defender and attack. Jump shot is irrelevant.
As a PF, I love Gordon and may even consider taking him over Wiggins #1. As a SF, I'm not in love with him, and I'd take Wiggins, Parker, and maybe Embiid and Exum over him.