Hangouts is also a messaging app that is meant to replace texts.
True, but the only thing I've ever heard it praised for is how well it handles multi-person video chats. I've never heard of anyone using it for purely text chats. Maybe that will change, but it's not an SMS replacer yet at any level.
Neither is What's App
Of course people use hangouts for purely text chat -- it's Google Talk!
Yep, my company uses Google Talk for IM, so as a result most of us use the Hangouts app if we want to chat on mobile.