There is not even one Chromium (or Firefox) based browser on iOS because it's not allowed to publish other browser engines on iOS!
It sounds like the EU and others may be fixing this soon by forcing Apple to allow other app stores on their devices if they want to continue selling devices in their regions.
Presumably Amazon store / Epic store / etc on iOS will carry real Firefox / Chrome.
The point is that Firefox and Chrome on iOS are not the same browser as Firefox and Chrome on any other platform.
For example, if I get a bug report from someone saying they're using Chrome on mobile, if they then say they're using iOS, that's a whole different kettle of fish from any other Chrome bug report I might get. It's going to be much closer to a Safari-related bug than a Chrome one, in a conventional sense.