Those 12-16 minutes each game are pretty important, and the drop off without Favors is drastic. Harris does seem like an obvious upgrade offensively as a 4 in today's NBA over Favors, but this isn't a single-variable decision. Hypothetical:

Jazz are 9 PPG better with Harris at PF over Favors. 16 MPG = +3 points
Jazz are 12 PPG better with Harris at PF over Niang. 16 MPG = +4 points
Jazz are 15 PPG better with Favors at C over Bradley. 16 MPG = -5 points

Obviously those are not real numbers, but I think they are reasonable for a hypothetical. So Harris over Favors straight up makes the Jazz about 2 points better per game, which is nice. Is that enough to give up Ingles as well? My answer is no.