You mean like Anthony Davis is a specialist?
Davis is a power forward who for his career is averaging 1.6 three-point attempts per game and making 31% of them. That comes out to about one made 3-point shot every two games.
His second and third years he combined to go 3-for-21 from deep, but somehow made the All-Star team both years. So to say "whether [Mobley] plays the 5, the 4, or the 3, he needs [the 3-point shot]", isn't correct. Joel Embiid, a center, averages 3.5 shots from deep a game and makes 33% of them, so he makes about one per game. He's been an All-Star four years in a row.
The guy I've seen Mobley compared to the most is Chris Bosh (6'11", 235), who averaged 1.0 three-point attempts per game in his career. Bosh managed to make the All-Star team 11 times despite rarely putting up a 3. Nobody called him a specialist.
The Cavs just gave Jared Allen a $100 million contract. That's pretty good money for a specialist.
