But they were kind of asked to do different things, no? Tai came in playing mostly PG, on a team with three volume scorers. He wasn't asked to jack up a bunch of threes, especially early in his career, and was at BEST the #4 option behind Petteway, Pitch, and Shields. His early role was really one of taking care of the ball and playing D.
Jack came in as a shooter. You can live with his shortcomings on defense as long as he's making up for it on the offensive end. If he was a lock down defender and solid ball handler, then his shooting slumps would be easier to pallet...but I don't think it's a stretch to say that he is both a below average defender and below average ball handler.
There's still absolutely a role for Jack on this team, and hopefully a large one where he's draining treys. But I don't think comparing his statistics with Tai's proves that.