The upside is the user experience for iOS users using SMS was dogshit. Apple dragging their feet didn't just make the user experience worse for Android users who texted iOS users, it also did the same to it's own iOS users. Hell, it even made it terrible between iOS users when iMessage had to fallback to SMS when there was bad data signal and the video that was sent would arrive in some compressed video file that would have been right at home in 1998.

This whole time we could have had typing indicators, read receipts, higher quality photos and videos, well functioning group chats... etc, between android and iOS (and among iOS when there was not data) but instead we just had shitty SMS/MMS technology from over 20 years ago. Apple kept things intentionally worse for it's own users to create a sense of "lock in"