It's true that if nobody you want to talk to is on it or willing to install it, then it's not of much use. It's also a bit harder to find really compelling features for direct messages. Though even for DMs, outside of Apple's walled iMessage garden, it's hard to get stuff like high quality photos, videos, and audio messages, reactions, stickers, etc that work correctly for everyone on all device types.
Group handling is where all of the apps really shine though. Doing groups in SMS is basically garbage compared to pretty much any chat app ever made.
