Randle had four impressive games last year, Seattle, Chicago, Commanders, and Jags. Three of those games came when Murray wore down the defense. He also had 50 carries, not hard to have a high average with that amount of carries. Look at the statistics, against Houston he a 2.2 average, against Giants, 3.5 average, against Arizona a 2.0 average, against Philly 3.0 average, against Indy (On 13 carries, his most in a single game) he had a 2.8 average. It's easy to have a high rushing average when you have games where you averaged 17 yards on limited touches.
There certainly was a dropoff between he and Murray, and defenses were far more keyed in on Murray.