Pat Kirwan has said for years that having a big three (dynamic RB, versatile TE, strong X) is what allows teams to abuse defenses. There’s a legitimate run/pass threat on every play, and defenses don’t have enough guys to keep all three guys in check. Someone is getting a plus matchup.
You could argue that Shanahan has a big five with the inclusion of versatile players at Z and FB, but they needed a dynamic RB to completely unlock that group. We are lacking a versatile TE, and are currently accepting applications for a strong X.