Monolithic apps suffer from design for the least common denominator. Business team chat and calling/texting your friend are entirely different problems and deserve different solutions.
I would suggest you check out Discord, which works well for both the team and individual use cases in one user interface. The way they accomplish this is by having "Friends" (a familiar analogy for anyone who has used chat applications from the 2000s and current social media) as well as "Servers", which are akin to teams.
Joining servers is very easy, creating servers - they are perhaps inaccurately named - is instantaneous, and each server can contain groups, voice and text channels. Adding friends is easy, and from the friends menu it's easy to message or begin a call with anyone and create ad hoc group chats and calls.
Perhaps your belief that they are entirely different problems and necessitate different solutions is based in the fact that they the market has thus far assumed that to be true.
I've used discord. My family is never going to use discord or a discord-like app. For that, we need sms or MMS.
One of the problems with discord is that it becomes very bloated to use (fromm mobile). It takes 3-4 interactions to get to the friends list so I can message someone. With sms/mms/allo/fb messenger, I open the app and my friends list is just right there, staring me in the face.
Hmm, my version of Discord either points me at the friends list or restores previous state with 2 or 3 taps max to message a friend. (top left hamburger menu, tap friends, pick a friend)
I was speakng about android. I think there's a vast difference between 0 and 2-3 interactions. I mean in many ways, Discord is 2 apps in one, you swap between them by swapping between the servers and friends views, and I think its worth recognizing that fact.
Why would an Allo/Duo user ever want to join a server, or something analogous? They just want to call or message their friend. I think it's obvious to merge some of their consumer point to point apps, but criticizing their group chat solution because they have consumer point-to-point apps is wrong.
Do you never want to talk to more than one person? I don't see why talking to one person is one app but adding another person means we need to stop, hangup, open a new app and reconnect.
But Google doesn't segment their chat products based on target market, they segment it based on business unit. Google is just really unafraid of competing with Google in the marketplace, apparently.
OK, so here is consumer case: weekly video call to parents, who live separately. Duo? 1-on-1. Hangouts Meet? enterprise. Original Hangouts? Who knows how long it will be here, but hey, Google Voice suddenly got updated after 5 years of neglect. Doesn't get any more clear than this.
I think it is an uncommon use case, but I wouldn't say exotic. On the other hand, which of the latest services support it? WhatsApp doesn't, FaceTime doesn't (although they're rumored to soon). So I'd guess it isn't common enough to be launched in the initial versions.
On your second point, yes, you're segmenting by use case, I was segmenting by target customer.
Joining servers is very easy, creating servers - they are perhaps inaccurately named - is instantaneous, and each server can contain groups, voice and text channels. Adding friends is easy, and from the friends menu it's easy to message or begin a call with anyone and create ad hoc group chats and calls.
Perhaps your belief that they are entirely different problems and necessitate different solutions is based in the fact that they the market has thus far assumed that to be true.