@Awi,
I hope we talk about SPPB 5.2x, not older versions. If yes, Image addon has two fields for images. Classic one and 2nd for Retina screen. Our component support webp format, that is better than old jpg.

But I assume that you talk about sort of thumbs image, but for what resolution of screen. Because now smartphone screens are much larger than was 5-6 years ago. And the resolution of the tablet, iPad Pro resembles a small laptop.
if you can share example of popular site where that solution used, I would have an argument to discuss with our developers. Just share links where I can preview HTML code, I would appreciate it.
OR maybe you thought about Srcset HTML image attribute that specifies the list of images to use in different browser situations.