There's still a huge advantage for Electron - it's still fundamentally the same tech underneath - HTML, CSS, JS. Any semi-competent web developer can use Electron and ship cross-platform apps with it, and heck, lots of code can be shared between Electron apps and the web "app". None of the other options provide these facilities.
But, you then have all the problems with JS/HTML/CSS that web developers have. Like for example being able to support scroll bars and the like in a reasonable way. We accept certain poor behaviors from web apps because they are bound by a technology stack that is in many way sub optimal for the needs of the user.
I was employed doing what we called client server development in the 1990's, where we wrote the frontends the users interacted with in vb and later delphi. I would put the visual and operational complexity of some of those applications far beyond any slack/etc type application (one actually had a chat function built in). They were also distributed, but instead used proprietary protocols over proprietary wireless networks (until later when we were some of the first customers for cellular data). And I say it not to brag, but there were two of us working on the front end, both part time over the span of maybe 5 years. And we could do large logs/chat histories where the scrollbar reflected where in the data set the user was viewing and they could smoothly scroll or jump to any arbitrary location. I can't remember the last web application that could do something even that basic. Slack definitely cant. I'm pretty sure there are more developers working more hours on the slack front-end than we worked on those applications. So, I'm not sure where the claims of developer efficiency comes from.
People make a lot of claims about developer efficiency, but just about none of them are backed up by more than their gut instincts, which I would claim from the end user/3rd party viewpoint seem to be completely invalid. The apps are overwhelmingly poor on any number of fronts, and apparently have a lot of man hours poured into them.
