How the players are used is almost everything. Hayward was exceptional in zone and he is being used to his strengths in SD. He also got to face two interception machines yesterday.
McCarthy does not have a system that is easy to operate out of the box. It requires time to customize and he tinkers with it weekly. Just look at what he did to Hundley after the relative Chicago success. He pulled the run run pass offense in favor of pass run pass. And that got worse after Mays fumble.
Sometimes McCarthy forgets about the player and only thinks in terms of strategy or tactics. He has not adjusted to Hundley while Hundley is still adjusting to him. Quick change of scheme isn't a feature of this offense.