The default chat app and the technical merit dosn't matter. What matters is what people we want to chat with. Most of my friends and groups are on WhatsApp. Some prefer to use Telegram, me too. A very few living outside the country use FB Messenger. Nobody use SMS unless for emergencies, if they think the recipient has no data connection. RCS is totally unknown. If I say RCS somebody will ask me "the newspaper company?"
Making people switch is possible (use Telegram to chat with me), making a group switch is impossible as there is always at least one person that doesn't want to install a new app or can't (phones with tiny storage.) Anything else is irrilevant in my country. There are probably some friends of mine using iMessage when chatting with somebody they know to have an iPhone. They still to have to use WhatsApp to chat with everybody else.
Making people switch is possible (use Telegram to chat with me), making a group switch is impossible as there is always at least one person that doesn't want to install a new app or can't (phones with tiny storage.) Anything else is irrilevant in my country. There are probably some friends of mine using iMessage when chatting with somebody they know to have an iPhone. They still to have to use WhatsApp to chat with everybody else.