JPEG XL may solve all these problems instantly:
It is a progressive image format which has an amazing feature: you can terminate the bitstream at any point during the download and have a good looking image. So servers could keep the high resolution of an image but send over just the first (for example) 20% when client is on mobile, and send 50% of the file for laptop, and all 100% when users are on a 4K television.
https://cloudinary.com/blog/time_for_next_gen_codecs_to_deth...
https://cloudinary.com/blog/improve_the_web_experience_with_...