The key glue to a lot of what you mentioned missing in your list to make a lot of this work for outside consumers: API Gateway, arguably their worst product.
I agree, they really need to replace that product. It's not built to the standard that users expect from AWS. They have burned a lot of goodwill on that one.
That said, it's only truly necessary for Lambda and while it's frustrating and painful there, it's usually not a complete showstopper.
