I’m fully behind the idea that you should be able to opt for not downloading the biggest texture files and 3D assets, if you’re gonna play at low settings, anyway.
But it’s worth noting that “optimizing” the file sizes of high-fidelity games isn’t really possible. You can’t compress textures or 3D assets the same way you might an RGB image. Game textures contain a lot more layers than just color, in modern games they can contain material, depth and specularity maps, just to name a few. And that’s before considering any accompanying bre-baked lighting data that entire levels may come with, which trades in the need to real-time render stuff for doing it in advance and storing how something is supposed to look, and shipping it alongside the game.
None of this can be easily compressed. It has to be retained losslessly, or you risk rendering artefacts.
Also, most game distribution services will send you an AGGRESSIVELY compressed (as in packed as a whole, using great amounts of CPU to pack it smaller without data loss) format, which your PC/console unpacks as it downloads. They too have every reason to save bandwidth.
But even then, you seldom see data savings of more than 10-30%. There just aren’t that many corners to cut.