Are Views responsive on mobile devices?

Yes! Both Table View and DataTables layouts are responsive on mobile devices:

A Table View layout like this:

...will shrink to a vertical layout, so it looks better on mobile devices:

You can use this filter to disable this responsive mode: add_filter( 'gravityview/template/table/use-legacy-style', '__return_true' );

DataTables, on the other hand, has a special mode called "Responsive Tables", which you can read more about it here: How to Enable the Responsive Tables mode.