I don't think you can do that anymore, though. But I haven't tried it in a while.
A huge problem I see with the web is that it's is missing concessions for "advanced" users. I get that we're a smaller market, but come on.
I would also say money wasted on providing support for those users but I'm still not sure if such thing exists.
Oh course the "desktop" (not really) Hangouts app also only opens links in Chrome.
Don't worry though, Hangouts will soon be discontinued and we'll have to complain about some Google chat app.
On other operating systems you can set the default browser to be Firefox, Chrome, or whatever else you want, and different browser engines are allowed.
Chrome on Wayland, with GNOME 3 in particular, pretty much always pins a core too, but not for Gmail-related reasons.
I'd make the argument that the parent should not be down voted because Google, perhaps in a small way, allows degraded experiences on other platforms for one reason or another.