SMS, iMessage and now RCS have been working well for me and I’ve been (primarily) using iPhones for the past 8 years now.
The Messages app shows what type of message (iMessage/SMS/RCS) you’re about to send in the text field and displays which (sent or received) messages are what as well.
One thing I could see going wrong is that a given phone number is registered with iMessage and it hasn’t been disabled after switching to an Android phone for example.
Another (imo more likely) thing is that if it’s using RCS, some carriers don’t seem to work too well with it as of now. iOS seems to have implemented the base standard, while Google added proprietary extensions to said “standard” in Android, like end-to-end encryption. I never had issues sending or receiving RCS messages from/to Android devices, but there might be some hiccups for some people as RCS - even though it’s called a “standard” - isn’t really standardized.
Not sure what’s so insane from Apple’s side about any of that.
The EFI will control the fans just fine.