Yes they do...assistant coaches matter and they add greatly to the gameplanning, leadership, and philosophy of the team. Have you ever played ball on a team?
Doc Rivers hasn't had a top 5 defense without the G.O.A.T. defensive mind Thibs on his staff and its not because of a lack of personnel...
Mike D'Antoni had the Sixers playing at a higher tempo and their offense improved the second half of last season upon hiring D'Antoni as an assistant...
Tex Winter created the triangle offense and was assistant coach under Phil Jackson during the Bulls and Lakers championship years...
Hank Egan was the mind behind the mid to late 2000's Cavaliers defense he brought over principles from the Spurs...
Did you not just see Ty Lue get promoted from assistant to head coach?