The article compares the native (iOS) mail app which is (from the article) 8.7MB. What I believe is happening is that the gmail app is not a native app, it is some cross-platform monstrosity, so Google has to bring all the widgets and doo-dads that they wrote so that it looks just like it does on all the other platforms. The native iOS mail app is so tiny because part of iOS that the article mentions taking up 25GB contains all the native widgets and doo-dads that the native mail app can use.