It has become rare even in the NFL that one RB thrives and gets a vast majority of the carries.
The days of an Emmitt Smith or Barry Sanders carrying the ball 30 times a game are long since over. Derrick Henry is the closest we've seen of that style in the last 5-10 years and even he is sharing carries now (though he's having a bit of a renaissance with Baltimore).
I do hope to see Miller and Haynes carry the ball more as the year goes on, but realistically, it's going to be up and down depending on the defense. It's not something we are going to force anymore. That ended for Alabama, IMO, after Henry went pro.