In average, training = improvement. And in this case we are talking about 26-27 year old fighters who both are generally considered being close in their primes. Its logical to believe a healthy training time at this point in their careers has some value for both fighters. And Gus has been training more after their first fight. Its logical to assume Gus has more likely gained an edge in that apartment than Jones. Not sure, but more likely.
By your standards Nate Diaz is the most Improved fighter in the LW division