Unreliable courier makes Amazon unreliable

My initial experience with Amazon was extremely good, which is why it gets two stars. However, their choice of courier service, specifically The Courier Guy is awful for their business. Their next day deliveries are continually being delayed by up to a week- what is the point of using them if they deliver as slowly as their competitors, like Takealot? The courier service is going to cost them a lot of customers, because it makes them unreliable and slow. In the last two months I haven't had one smooth experience with delivery, and it's not okay anymore.