Imo it’s less about the speed than the predictability.

I routinely pick the “next Monday and we’ll give you two bucks digital credit or whatever” option because I assume it’ll make the shipping a little more efficient or make some factory grunt’s life easier, and I’ll still pick Amazon over other vendors because when they say Monday, they mean Monday.

I’m always able to track the shipment, it’s always predictable, I never have to wonder. It’s a less tangible feature but far more valuable.