One, comparing Elliott now to what he was in college is just foolish. He was younger, fresher, more explosive as a college player than he is now. Two, Elliott is the highest paid TB (by total contract size). Given the cap hits he's going to eat up, he has to be more than a bruiser TB that wears down defenses and then is effective after that 14th touch in a game.
Three, the Murray angle doesn't help your case here. In fact, it kind of hurts it. For one, the Cowboys came out and said after 2014 that they couldn't commit to the years and money Murray wanted because their data showed TBs drop off after so many carries and the kind of usage Murray had. And guess what? They were right. Murray was never the same after that 2014 season. He struggled in Philly, came back with a 1,200 yard season in Tennessee, but then fell back and was out of the league by 2017. You also conveniently left out to big storylines in 2015 - one, it wasnt just Randle they wanted to run the ball, they also signed Darren McFadden, who actually ran for 1,000 yards that year. The other issue was that it wasn't not having Murray that killed the 2015 season, it was that Romo got hurt and we had to play a majority of the season with guys like Brandon Weeden at QB. And think about that, McFadden ran for 1,000 yards (starting only 10 games too that year) and did so with crappy QB play.
If anything, the Murray thing shows it's more wise to invest in the OL than eat up oodles of cap space on a TB.