I think you will not be so strict and quickly use the iPhone for everything and the Pixel will become obsolete.
I came from an iPhone and switched to GrapheneOS.
And I can confirm that iOS is really a good OS and the usability is unrivaled by Google.
But, you can't restrict much about what apps can do or not. Apple has, like Google some settings to deny apps some features, but overall it's cosmetically.
In the end it's about if you want convenience or control about your data.
I think you should wait one or two weeks before you finally buy a phone.
Are you really this much dependent on rcs/iMessage? iPhones are great smartphones, but I wouldn't buy one only because of texting people. And maybe the rcs thing will get solved soon, it is not only Graphene having trouble with it, even stock android has problems.
So in the end you will not use RCS as much as you think, if it's down again on Google's side, you will send unencrypted SMS again.
So you can only be sure that iMessage works, but that can't send to Android.