The way I think about it is like this:

We want a representation that is as close as possible to what actually is in AWS. That way any proposed changes have a high probability of success when they are applied. SI's approach keeps an extremely up to date representation of what's in AWS.

Why do we need a representation and not just go directly to the AWS API? Among other items, it removes the capability of reviewing changes before they are applied. It gives us a safety net if you will.

We didn't recreate the AWS API. Rather than think about it as the API calls, imagine it this way. You have a real resource, say an EC2 instance. It has tons of properties, like 'ImageId', 'InstanceType', or 'InstanceId'. Over the lifetime of that EC2 instance, some of those properties might change, usually because someone takes action on that instance - say to start, stop, or restart it. That gets reflected in the 'state' of the resource. If that resource changes, you can look at the state of it and update the resource (in what is a very straightforward operation most of the time.)

The 'digital twin' (what we call a component) is taking that exact same representation that AWS has, and making a mirror of it. Imagine it like a linked copy. Now, on that copy, you can set properties, propose actions, validate your input, apply your policy, etc. You can compare it to the (constantly evolving, perhaps) state of the real resource.

So we track the changes you make to the component, make sure they make sense, and then let you review everything you (or an AI agent) are proposing. Then when it comes time to actually apply those changes to the world, we do that for you directly.

A few other upsides of this approach. One is that we don't care how a change happens. If you change something outside of System Initiative, that's fine - the resource can update, and then you can look at the delta and decide if it's beneficial or not. Because we track changes over time, we can do things like replay those changes into open change sets - basically making sure any proposed changes you are making are always up to date with the real world.