But on macOS you can switch to a browser that can do all these things. A company could ask you to use a different browser (not ideal, but if the web app requires a specific API, it's not an unreasonable).

Safari is in a very special position because it controls what the web can do on iOS (all browsers on iOS have to use Apple's WebKit engine, they can't add web features). Apple is not just gatekeeping native (through the app store), but its competition, too (the open web, through the webkit requirement)