Not true. You cannot set default apps. You can hide the stock Apple apps but that's it
Huh. I guess this is not doing what I think it does: https://www.imore.com/how-delete-apple-apps-ios-10
[EDIT] I see the fine print now, from that very link I referenced above:
when you delete them, they aren't actually removed — they're just being hidden from the home screen. (It's very similar to the toggle for Apple's iCloud Drive app in iOS 9.)