What is so awesome about iMessage other than the fact that everyone with an iPhone is on it, and therefore you have the population? You have more functionality and choice if you used WhatsApp, Line, or even Kakao, to be honest. My second phone is an iPhone XS Max and I don't get the appeal other than the whole green vs blue is some sort of status symbol - really one created in the minds of iPhone users. I can't modify the look of it. I can't change the notification sound, I can't mute a group conversation - I can't even look at all the media that has been posted to the group chat. So, to be honest - when I hear about how great iMessage is - I don't see it outside of the fact is that they have the number of users.
The population is what makes iMessage great. And that really makes it a US-centric thing. If I'm not mistaken, iPhone has larger market share in the US compared to Android.
Weird though - I can mute an iMessage conversation by hiding alerts and I can see all of the media (like photos, videos, links, and attachments) in the Info section of an iMessage thread. ¯\_(ツ)_/¯