You want to use our app, but you don't need real-time carrier rates, just basic rule based rates and rules. And, based on the title of the 'Calculated Rate' feature requirement, it makes sense that you may think/hope that you don't need the feature to use the app.
However, our app, or any 3rd Party Shipping App, is considered by Shopify to be a calculated rate, regardless of if you using the app to set-up carrier rates or not.
You can think our app as a 'design your own calculated rate'.
So regardless of how you plan to use the app, carrier rates or not, the Calculated Rate feature is required to use the app.
The feature allows you to connect our app to your shipping settings, and without the feature the app cannot be connected to your zones to show rates -- of any kind -- at checkout.