You can reduce the electron app size by packaging using electron-builder package.
PicArt is an electronjs app which I developed recently. It is built using reactJS. Initially when I packaged the app using electron-packager the Window’s build size was around 98 MB. Then I found this awesome boilerplate electron-react where they configured the electron-builder to produced optimised build size. After using those configuration setup, PicArt’s build is now around 36 MB.
Yes, it is possible to reduce the app size , but it quite painful and time consuming to configure the build setup.