Making the playoffs isn't a successful season. Making the NFCCG or AFCCG could be considered a success. Anything else, not really.
But let's play your game and look at last year.
Chiefs - 803, 254, 169, 123, 97
Bills - 687, 481, 70, 63
Steelers - 721, 368, 113, 65
Titans - 2027, 204, 95
Ravens - 805, 723, 299, 70
Browns - 1067, 841, 166
Colts - 1169, 380, 308
Packers - 1104, 505, 242
Saints - 932, 656, 101
Seahawks - 681, 356, 108, 88
WFT - 795, 365, 258
Bucs - 978, 367, 109
Rams - 625, 624, 419
Bears - 1070, 232, 74
So. Of 14 teams only 5 have what you would call a feature back or bellcow. I think you might try to argue RoJo was that guy for the Bucs but he wasn't. He got a bunch of those yards early in the season, lost a lot of carries to Fournette later. I had him in FF so the sadness still lingers.
Carson probably would have had more yards if not for missing some games but would have been 908 at the same rate. And the point is, they still made the playoffs spreading the load around.
If you want to do other years feel free but in todays game, a feature back just isn't crucial.
I'd still like a solid 3rd back before I'm happy with the RB room though.