We were building decent apps long before React.
Even pre-web. I remember, how quickly I could create Delphi desktop app with drag & drop UI builder more than 2 decades ago. If we speak about generic ERP, you could make dozens of screens in a day.
You just split your app to layers.
That might be for example:
1. Just UI;
2. UI logic (validations, preloading selects...);
3. Transformation of data between data model and UI model
All of the things above lived on users' computers.
All of the things below were on servers.
1. API gateway (terrible things like SOAP, XML-RPC or completely proprietary formats);
2. Business logic;
3. Database
Even pre-web. I remember, how quickly I could create Delphi desktop app with drag & drop UI builder more than 2 decades ago. If we speak about generic ERP, you could make dozens of screens in a day.
You just split your app to layers.
That might be for example:
1. Just UI;
2. UI logic (validations, preloading selects...);
3. Transformation of data between data model and UI model
All of the things above lived on users' computers.
All of the things below were on servers.
1. API gateway (terrible things like SOAP, XML-RPC or completely proprietary formats);
2. Business logic;
3. Database