From what I watched, Miami last year ran a successful RBBC. They had the power in Jeff Wilson/Brooks and then the shifty speedy backs in Mostert and Achane.
This year, they let Connor Williams and Robert Hunt walk and replaced them with hope and dreams.
Still got the same backs, and Wright-who looks to be good, but the line is ***.
RBBC isn't the issue with the run game. It's the talent of the running backs and a mix of growing pain with rookies and the decline of Martin. Every back on the team IMO isn't that good/there's not much variation between the backs.
They all are around the same speed/talent level.
Doesn't mean the team needs to draft a RB high, but at the same time, ignoring the position completely and re-signing Zeke & Rico wasn't the answer for a better chance at an effective run game.