You have the right ideas, and there are protocols that do this, some more isolationist than others: https://yesterweb.org/zine/issue-05/08/ "The Web Outside the Net" and https://wiki.archiveteam.org/index.php/SmolNet

Modern smartphones could implement more Data Saver features, but websites could opt-in by using less data. For example, https://marcusb.org/hacks/tinyblog.html