RCS is not modern. E2EE is only an addon and it's not open. As others have mentioned it's not even available with interoperation. And it was really invented by carriers for exactly that purpose: To regain SMS/MMS revenue. But at this point here in Europe SMS usage between people had vanished anyway (except for spam and poor 2FA implementations)
And the social problems are not a technology problem, it's more a result of the harsh competitive American society. Without blue bubbles there'll be something else that kids will be bullied for. Only when the whole concept of "everyone except the #1 winner is a loser" is dropped this will disappear.
And Google didn't try to convince Apple to do this out of the goodness of their heart. Like I said most of the protocol (except the E2EE) is open but the implementation is not. It gives google even more control. You also won't be able to use it on a PC without a google account which is a big dealbreaker compared to Whatsapp and Signal. iMessage isn't a thing here in Europe anyway (neither is SMS/MMS).
iMessage isn't a thing in Europe?
No not really. It's technically available but nobody uses it. Everyone is on WhatsApp. Even companies. I never get messages from contacts on SMS either (so it's not going through fallback). I think it's because iOS just isn't really that widely used here. Not used enough to have critical mass for an iOS-only messaging service.
At least in the countries I deal with in Europe (Netherlands, Spain, France, Ireland). Perhaps in UK the adoption is higher because they have more money and thus iOS usage is higher. But everyone I know is on either WhatsApp or Telegram (and sometimes but very rarely Signal). Also we are much more socially disconnected from the UK since brexit.
As a bit of added info, the reason SMS is so hated here is because providers offered paid SMS services. You could sign up for e.g. daily weather reports and you got billed for it on your phone bill. It could be up to 1-2 euro per SMS. Some countries even up to 5 as far as I remember. This service was abused a LOT by scammers who just signed people up without consent and refused to remove them. The carriers did almost nothing against this because they were raking in the euros. This caused people to be very wary of SMS. Most people I know never use it anymore. They get worried when they receive something because they are afraid they'll get charged. Which can really add up if they do it from the start of your billing cycle. So its use as iMessage fallback is also pretty nonexistent.
So this is also why I am so wary of RCS and the carriers. They have played a deplorable role in the 2000s/early 2010s. Really cashing in hard with small bundles and insane out-of-bundle charges for SMS, the pay service scams etc. It was really their cash cow. So my trust in them is forever lost, I will never trust them to provide more than just transporting neutral bits from A to B.
It's also why I will never sign a contract with telcos and always use prepay. That way they can never take more of my money than I have in credit.