The DM's responsibility, their "job", is to ensure the players are having fun. That doesn't "only" mean to be rigid and to exercise might. It means to make sure that the players are enjoying themselves and getting what they want from the session. If one player likes to feel like they have control over certain things, like how a particular spell works, then it's up to the DM to help that player "feel" as if they have the level of control they desire...without necessarily giving the player that control.
Bottom line, are the players having fun? The DM adapts to their players, just like the players adapt to their DM. When it's done well, everyone has a good time. The core rules are frankly borderline irrelevant. It's the people around the table that determine whether a game is good, not the rules in any rulebook.