Nylander is 3 years younger and producing better.
last 2 years combinded:
Gaudreau: 104 GP, 31 G, 52 A, 83 P, for 0.3 GPG and 0.8 PPG
Nylander: 100 GP, 43 G, 40 A, 83 P, for 0.43 GPG and 0.83 PPG
so he has goal scoring, age, and term on his side. absolutely a more valuable asset.
Mangiapane isnt that much better than Kerfoot. their PPG's over the past 2 years are similar, Kerfoot 0.43 and Mangiapane 0.48. plus Kerfoot is a C. its not significant. what makes him more valuable imo is his RFA status. but lets not act like he is a significantly better player right now.
so all in all the gap in value between Kerfoot-Mangiapane doesnt make up for the gap between Nylander-Gaudreau.