One of the things that often gets overlooked in trades is how a team perceives diminishing returns.
We tend to look at things in the context of the immediate aftermath of a trade. Who's scoring better, etc.
But a big part of the discussion is about how things look 2 or 3 years down the line. How does their contract look, how does their value look, where is the team at, how does a certain player look on a team at that point.
So the question for the Rangers isn't about how Miller looks playing next to Stamkos and Kucherov on his new contract, or how McD looks playing on the second pair and being one of the guys.
The question for the Rangers is how Miller looks playing on this team, with these players, on what is likely a higher contract, or how McD looks plugged in as a first pair defenseman, and a captain, and having to be more than just one of the guys.