I don’t see those as alternatives. Skype was always really buggy, sometimes it worked, other times it didn’t. Didn’t have great cross platform support and wasn’t suited for meetings without 500 - 1000 people. I used it in the past and it was always a huge pain to deal with.
Hangouts is nice for 1:1 chats, but it feels lacking. Last time I tried to have a screen share in a separate window it already failed to do so.
Discord isn’t really an enterprise tool.
Like… I don’t really want to defend Zoom, but the one thing they do just works.
One thing though: I’m likely not to stop and consider looking closer at an app if I can’t judge if it’s going to be what I’m looking for. I’m not going to go over random GitHub repositories and create screenshots for their projects. So if the assumption is that the user contributes screenshots I don’t think it will ever change anything for the majority of projects.