Samsung alone is ~25% of the global Android smartphone market share [0]. This means 1 in 4 Android users will send “SMS” messages via RCS. You’re right, it’s not actually default, but it may as well be considering the app has over 5 billion downloads [1] and over 800 million monthly active users (MAU) [2]. This makes Google’s Messages app slightly more popular than Telegram with 700 million MAU [3]. It may be a recent change, but its already taking over some of the more popular apps in terms of usage and general availability.
RCS is is late to the game but it’s caught up and only getting better.
[0] You’ll need to subtract Apple from the market share total to calculate the 25% as they include Apple in these numbers and I’m only talking about Android devices. Source: counterpointresearch.com/…/global-smartphone-shar…