That's a great point, but I'll take it further. Even if you know how to build all that stuff, you still have to build it, there are a lot of decisions to make

That's a great point, but I'll take it further. Even if you know how to build all that stuff, you still have to build it, there are a lot of decisions to make up front. Depending on the company (Stripe comes to mind), I might choose to trust the SDK's decisions by default and only move away from it when I have specific pain points. A lot can be solved simply by isolating the SDK's usage inside a wrapper that defines our application's usage of the SDK.