as far as i'm aware, it can still be made to work without special accessibility events. other password managers are able to correctly fill in credentials in these browsers.
some of them have public source code (GPL licenced) which show how they do it.
some references: code which detects the URL fields in browsers if it detects an application name that's a browser in it's list (it's a xamarin app, so it's c# code):
https://github.com/bitwarden/mobile/blob/master/src/Android/AutofillService.cs#L260
list of browsers and corresponding urlbar field names: https://github.com/bitwarden/mobile/blob/master/src/Android/AutofillService.cs#L24
so this should definitely be possible to implement.
i understand that the current implementation might have some limitations, but you should still be able to work around those limitations by detecting the URL fields in the apps.
kind regards
intuxikated