When I lived in the Bay Area Amazon always delivered as promised. I even got same day delivery sometimes. Now that I'm in the boonies, I think they are the whim of the delivery services. I'll get many things in 2 days, then something I'm counting on arrives in 5. I consider that an issue with living in the boonies.
The other thing to remember about Amazon - yes, they are huge, but they have a really unique system. You may be buying from Amazon, but most of their stuff is through other vendors. They actually do provide a good platform to sell things for the smaller business and a way to reach more people. Since moving here, I'm thrilled to have a way to get many of the things I can't get here.