Not quite:

- Facebook Messenger combines all the functionality of Allo and Duo. - Whatsapp already has voice calling and is adding video soon (so I read on the internet) - iMessage and Facetime integrate in IOS much better than Google Duo does. In IOS, you go to a contact and press facetime. On Android, you go to a contact... then go back out to Duo and call them.

WeChat, of course, does everything that all these apps will ever do - as of many years ago.

Duo competes with Facetime, except it's not integrated in Contacts and I can't imagine why. Duo and Facetime don't compete with Skype because they don't have the IM part which is a very important component of Skype. I used it for all these years as an IM client (business or friends), less as audio and rarely as video. But video is always the least used form of communication. Still I'd like to see some global usage stats of Skype: minutes by chat, voice, video. My customers, friends and I could be the outliers.

but hangouts lacks things which are useful for enterprises such as video recording (it's possible only if you make a "hangout on air", afaiu) and, in my experience, screen sharing text/code is painful because of the video encoding making it unreadable.

To me hangouts looks like a competitor to Skype only, at this time.

Except that Skype can be used for text chat like Allo.

And Apple doesn't really treat Facetime as an app.