The 49er run attack might be weaker this year. Deebo probably made the Niner coaching staff to think Mostert was expendable. But Deebo is a WR not a RB. Mostert was IMO the scariest RB on their roster. This guy had true explosion, as a RB with elite speed. I'm glad he's in Miami now. They also lost their starting RT and LG in Compton and Tomlinson. It's a matter of how good are their replacements? LG is key in pass protection and RT is a key in their run game.
If I had to speculate I'd say the 49ers got weaker, not better this year. The Cardinals also appear to be weaker as well. The 49ers draft fairly well but IMO the Cards had to resort to hired guns because they draft poorly. They only have about $6.5M in cap and they are notoriously poor in their cap management. Their roster isn't as strong as last year IMO.