I totally get the fragmentation, I asked in some techy groups if they prefer matrix, signal, wire, anything. Virtually nobody knows anything but telegram (because we were currently on tg) and facebook messaging systems. So I made a choice and now the tg side is dead and the new platform is missing some people... yup fragmentation at work.
But at that moment a choice for a new system was made, it's not so much about doing yet another move right after the previous and fragmenting it further. Any particular reason you didn't try Wire in the first place, if you don't like the phone number requirement?
Despite a really good uptake, some didn't make the move and it's definitely fragmented some of our online groups (makes it more interesting when physically catching up though, silver linings!). I'm not sure throwing yet another messaging platform would help.