It was not Electron's problem.

The problem was the extension architecture, that they leaned into heavily. It encouraged basically every part of the system to interact with every other part of the system, like having free reign over the whole DOM. That's what the creators meant by a "hackable" editor.

VS Code is much faster, largely because of its much more sane extension architecture. Extensions are much better isolated, with a much smaller API surface by which they can interact with the editor. And the LSP design means core IDE-like features can be lifted into a privileged part of the system, and implemented once with performance in mind, while the actual analysis is done asynchronously in subprocesses.

If you actually use both Atom and VS Code configured to feature parity, you would notice that VS Code is miles ahead of Atom. Microsoft did an amazing job proving that you can build complex performant software on Electron.

Yes, Electron 2.0.0 was a great update, but it's not the reason for performance. The reason was better software architecture.