You can't be great at every position. And great costs money and cap space.
Is RB one of the priority positions to be great at, and to spend the bucks to have, in order to win a Superbowl?

I say perhaps in the modern game, RB is not the place to acquire, and pay for, great. Maybe that same money would be better spent on a great TE. Or a great LT. Or a great WR. Or a great pass rusher. Etc. Assuming you can't have all of those (or other) positions stocked with HOF players.

So since a hard cap makes it a zero sum game, might it be better (if the goal is to win a Superbowl) to trade a great RB for a great something else?
It is a given that you need a great or near great QB to win (although there are occasional exceptions... Flacco for instance).

It's just a discussion. I'm not trying to convince anyone that the the right move is to trade Gurley. But to just dismiss it doesn't lend to the debate.
I've watched too many teams win lots of games during the regular season but bomb out in the playoffs (KC for example). Why? What's missing? Are they great in the wrong places and deficient in what matters when all is on the line?