I maintain an app size inspection tool that runs locally on your macOS and added the file inspector (Sunburst chart) for Gmail if anyone is interested in exploring its contents.

As others have pointed out, the main executable is huge (~300MB) and there are a lot of localization files, but not too much traditional asset duplication.

You can click into different slices of the app and see what it's made of if interested: https://dotipa.app/?app=Gmail#examples