Blocks are only available in the Block Editor.
GB only writes the CSS it uses on that page. If no GB blocks are added then no CSS is generated. And it requires no JS.
The Dev site generates 500 lines of GB generated CSS on the landing page, this can be minimzied further with GB Pro and Global Styles.
To put that into perspective, BootStrap adds over 10,000 lines of CSS whether you add one element or a hundred, plus it adds a couple of thousand lines of Javascript…..