In this Mattison hypothetical, what happens if Mattison is a ~top 8 RB for the first half of this season? Not only would it help his new owner (dropping the likely landing spot and thus the value of that future 1st), but Mattison could very likely then be traded for much more than one random 2025 1st.
And what if the Vikings bring in Zeke and/or play McBride and Ty Chandler a lot more than expected? What if the Vikings pass 20% more?
What if Mattison turns out to be merely the 24th? Best running back?
That hypothetical cuts both ways. If you trade Mattison today for 2025 first round pick, and Madison turns out to be not that great, you realize a profit matter what happens with that pick.
If playing the odds, it seems a lot less likely that Mattison will be a top 5 RB than say, the 15th best or 20th best RB.
Meanwhile that 1st round pick can’t change more than maybe 4-5 spots in either directions. So while not 100% immovable, certainly less volatile than a RB.