What's wrong with continuing to use SMS exactly? Why do we need to use alternative incompatible protocols if existing protocols are reliable and work even of 20 years old devices?
Both iPhone and Android support SMS and I see no improvement in either using iMessage or RCS. I may be biased because I don't use neither of them.
The only reason (from my POV) to stop using SMS, is that it is a security nightmare (no integrity or authentication, can be MITM) and for some crazy reason everyone has decided it is a splendid idea to use it for 2FA.
That is like using wolves to protect your sheep -- sure if you keep them well-fed it might work...
Otherwise, Google is complaining because iMessage is a moat Apple has, that Google can not break on its own.
How exactly does RCS fix the security issue? The texts are only E2E when both users are using the Google messaging app, plus group messages are just plain text
Both iPhone and Android support SMS and I see no improvement in either using iMessage or RCS. I may be biased because I don't use neither of them.