I mean these are the last season on their respective ELCs for Aho and Marner
Aho - 82GP, 30G, 83pts
Marner - 82Gp, 26G, 94pts
Both got 5 years but it took an offer sheet for Aho to get 8.5 vs 10.9 for Marner. You could argue more for Marner but I don't see how you could possibly argue the winger with 11 more points should get 30% more than the defensively responsible centre with more goals.
Contracts aren't based on one year, and their raw points in that final year also don't very accurately reflect the difference in their offensive impacts in that year. Just quickly...
Through their ELCs:
Marner vs. Aho
0.93 vs. 0.81 points per game
0.90 vs. 0.76 points per game (no EN)
2.39 vs. 1.94 points per 60 at 5v5
7.19 vs. 5.37 points per 60 on the PP
Final season:
Marner vs. Aho
1.15 vs. 1.01 P/GP
1.06 vs. 0.93 P/GP (no EN)
2.87 vs. 1.99 P/60 at 5v5
5.94 vs. 5.85 P/60 on the PP
Marner also got 6 years, not 5, so it's not a straight 8.5m to 10.9 comparison, and Aho was not more defensively responsible or a better goal scorer.
Both PKed, but not very much at that point. Both were given offer sheets.
And I mean, all of this is pretty irrelevant anyway, because while we could discuss how much better and more valuable Marner was than Aho through their pre-signing period, the fact is that there is no way to argue that signing an offer sheet with another team is taking less to stay in Carolina.