I am still confused how Zoom ended up being used this much, especially by less technical people. The UI is not intuitive at all, the options are a mess, and the product doesn't even know what audience it's trying to cater for. Every other Zoom call I've been in someone is having a technical error or confusion (even technically-inclined people).
That considered, at least in principle, it shouldn't be that hard for a competitor.
Everything else was (and most still is) much, much worse.
It somehow disappeared from communal memory, but before Zoom, it was common for the first 10 minutes on any group skype/hangout/webex/gotomeeting call to be all about making sure everyone is heard and seen.
And with Zoom, it went down to an acceptable 1-2 minutes or so. Others have slightly improved their game since, but not much -- I still occasionally get Meet/Hangout invites for work and there's often problems, mostly related to authorization/authentication and occasionally video/audio feed.
Zoom is bad. But all the competition is still worse (and used to be much worse just a few months ago).
This does NOT come without cost - e.g. their MacOS "just works" setup was incredibly broken from a security perspective, to the point that apple pushed an OS update to block it. But people don't care - convenience consistently trumps security in any mass market system.
It's funny because I went back to school but worked as the printer guy within an IT dept for about 5 years before deciding to go back to school. Our dept kept going back and forth on what video conferencing we should use for our meetings for about 2 years, they just couldn't make up their minds. Not once was zoom ever mentioned. I was kinda shocked once schools (everyone almost actually) started universally using zoom because that's the first I've heard of it and I was aware of at least half dozen other options.
The UI is complicated, yes. But the actual video calling is better than I've experienced in any other product.
Google Hangouts/Meet invariably slows down my whole machine and causes the laptop fans to spin up. Zoom never does that. And the video streams in Zoom have higher quality to boot.
I think also the UI is complex because of all the different use cases Zoom can be used for. I work for a Deaf school where it is not uncommon for >50% (if not 100%) of participants in a meeting to use sign language. While Zoom is not perfect for this use case (it has many defaults which assume people want audio) it offers many features which makes it easier to manage meetings. The most complex meetings we have are when there is mixed-mode (e.g. some people speaking and some people signing) where we have someone speaking and the video spotlighed onto a interpreter OR video spotlighted on to a person signing but with audio coming from the interpreter voicing for the signing person. This is a specialised use case I accept, but one Zoom handles out of the box really well. As a result the Deaf community have taken on Zoom for pretty much everything--from professional meeting all the way through to using Zoom for home catch ups with friends/family. Hangouts for some reason doesn't really do this very well--and in addition to the poor video quality (making it hard to see people signing) the Deaf community have pretty much sidelined Hangouts and other products.
We tried to go with some other services, but the number of groups we deal with that use zoom forced us to switch to zoom. It is good enough to work got non-technical people. The only real bug has been the microphone but turning off the auto adjust seems to fix that.
I have a 100/20 connection and Zoom is the only one which manages to stream 25 people in gallery view with very good quality without dropping a frame. It is so good if anyone has glitchy video, everyone knows it's a problem on their end and nothing to do with Zoom. The only other platform I've had extenstive experience with is Google Hangouts which has hugely pixelated video which stutters really badly and/or just gives up streaming video in meetings of <5 people. Any more and it just gets worse to the point video is literally like watching a really badly pixelated stop motion film. I work inside two different organisations--one using Zoom and the other using Hangouts. The Zoom-using organisation has people right throughout singing Zoom's praises. The other org using Google Hangouts complain bitterly about it and wishes they were using Zoom instead. YMMV of course.
That considered, at least in principle, it shouldn't be that hard for a competitor.