While I understand your shared-memory argument, Electron in this example, is using twice what Firefox is using for 3 webapps and another dozen tabs.
Three Web apps and 12 tabs might not be the equivalent of that one app in Electron, if it's a heavy one. If a Chrome browser instance running Slack uses less RAM than the Slack Electron app does, __then__ we can say Electron uses more RAM than it should.
I'm not saying it does or doesn't, and I'm not defending it, I just think we need to be a little more fair with our comparisons
I did a comparison a while back (though I'd hardly call it scientific). I built a basic "hello world" Electron app, which consumed 69MB of RAM on Windows 10. When I opened the html file of that app in Chrome it took 82MB.
Think of electron as a single tab open in a browser instance. If you open 12 tabs in chrome, it doesn't use 12x the RAM, because most of the initial RAM is used maintaining the browser instance, not the rendered tab. most electron apps don't have "tabs" but if they did they wouldn't multiply the memory usage either