If, like me you are forced to use Hangouts for work, not only are you forced to install Chrome but any links in Hangouts automatically open in Chrome not your choosen default browser because Google knows best.
I am not sure which world you live in. Hangouts by default is a web app / website, so you can still use other browser to open Hangouts, meaning you are not really forced to install Google Chrome at all. Hangouts just opens whatever link you click on whatever browser you are currently opening in.
If you however use the Hangouts app, clicking on links will make your device ask/ or open the default browser you have set in your mobile device. If you don't have the google chrome app at all, it won't open the link in google chrome.
If you got Hangouts through Google chrome app store, well it should be obvious why Hangouts would then open all links in google chrome.
This post is not trying to say Google don't do "this kind of stuff for years", but they do it differently and not the way you've said (google chrome defaults to gmail sign in page, google.com recommend installing google chrome, gmail has quick app icons with Hangouts, etc.).