On the desktop you are developing against a runtime that the developer of the app gets to choose, so why not choose one that has less potential for quirks?
Especially on macOS, where Chrome/Chromium have historically been extremely inefficient, swapping the Chromium engine for WebKit2 WebViews would mean battery, memory, and CPU savings which would absolutely be worth the effort IMHO.
That Slack, the poster child of bad Electron apps performs so badly must therefore have different reasons. Exactly the same way you can write websites in a way that is more or less efficient you can write Electron apps of varying degrees of efficiency.
To me, develop for Electron is more fun than normal web because I don't have to check whether the new web feature I am using is available everywhere (especially Safari) yet.
Good, then developers might start to develop against standards instead of handpicked browsers. Or if they use a future (unstable) standard that is their own headache (as opposed to user’s; which are subsequently in practice forced to use chromium derived browser).
An app developed against a single browser (as opposed to the web standard) should be considered what it is, an ugly hack, and developers that do it should only do it for their own private apps never to be published until it is standard compliant.