You can think a 5-person team can build highly performant native apps for a number of different platforms in a matter of months?
Sorry about everyone complaining about CPU, but Slack won the chat wars in part because they were early adopters of Electron, and got plenty of developer productivity benefits out of using the web stack to build on.
We're talking about a chat application for diverse corporate teams. If you don't have native apps for Windows/MacOS/Android/iOS at the get-go then you've missed the boat.
If you build it, they will come. Especially if they don't have a choice. So build the new, deprecate the old.