Most of them are, yes. AppImage also solves this, but doesn't have as robust of an update/package management system
AppImage is basically a fancy zip file. It's still completely up to you to make sure the thing you put in the zip file will actually run on other people's system.
Yeah, their Linux guy obviously didn't know what he was doing.
Google Earth was released in 2001, and Flatpak in 2015. That's a 14 year window of time in which this wasn't an option.