When I am using Export As with multiple layers selected, changing the export options like file type only applies to the selected image. There is no way to select multiple items in the list of files in the Export As dialog. Surely I don't have to change the settings for every single asset individually?
You do need to change it for every selected layer in the dialog because the dialog does not support multiple selection. This is something we have fixed and will be showing up in a future update in a few weeks.
If the settings you are making are for the same filetype, you might look into using Quick Export. You can change the settings for Quick Export in your Preferences. That will allow for a one click export.