The 2018 Stack Overflow Developer Survey [1] puts VSCode at almost double the number of developers compared to Atom (34.9% vs 18%). You're right about the package count: atom.io lists 7654 packages, compared to 6802 at marketplace.visualstudio.com, many of those being color themes (some seem generated and machine-published, too). That said, workflow for extension authoring in VSCode is amazing, the community is very much alive, and sometimes it almost feels like there's an "extension for everything". Quality may vary, naturally.

[1] https://insights.stackoverflow.com/survey/2018/