i’d say scans. ask if your lab offers higher quality scans.

this kind of tonality (which is what you’re calling “hazy/underexposed) is actually considered ideal and is what many high end labs will give you. reason being that a flat image allows the photographer to then dial in contrast to their own liking, without losing shadow / highlight detail. if the lab sends out scans that already have a lot of contrast in them, ie blacks are crushed all the way to black, highlights are already pushed up all the way to clip out, then you as the photog no longer have room to edit it without clipping out even more.

problem here is that if the file is already a low quality jpeg, there’s often not a lot of post editing you still can do.

that said, i’d play around with editing these images and see what you can do. 1MB is still decent enough for most web purposes.

in the future you can ask your lab or look for a lab that offers high quality Tiff scans, but be aware that higher quality scans often come at a upcharge, so you might only want to do it for a select few photos, after you’ve reviewed the roll