There is zero reason to switch browsers on iOS, They all run the same engine.
Safari also has extensions (which I believe 3rd party browsers can't use).
Eh, that's not true. Yes they run on the same engine, but there can still be different features overlaid on top, plus syncing history/bookmarks with your other devices.
The engine is by far the biggest part of a browser, but it is not the only part of a browser.
Also, EU users will soon have access to "real" different browsers.
Again, this is why this law was such a big deal. Prior to this you were correct. Thanks to the DMA, you are wrong. Firefox will be running Gecko, and Vivaldi, Brave, Chrome, etc are allowed to ship their flavors of chromium.