I feel its popularity is more to do with one stack everywhere, than say, some groundbreaking tech idea.
All that aside, I must agree. Electron, however you view it, has greatly boosted linux compat among popular applications.
No, frankly. Java GUI apps on Linux back in the day were often a complete disaster unless it was an open source app with a large Linux dev base. GUI apps had to be written for and tested on all the various platforms they were going to run on. You could probably run simple apps using the oldest lowest common denominator graphics toolkits working without specific support, but those old toolkits were as clunky and ugly as hell.
Electron is far more out of the box on Linux than Java ever was.