When you check the option to disable the lightbox, you should also be able to disable the link to the photo. I have never have my photos linked to the media file in the posts. It wastes link juice.
If you set the photo attachment pixel with wide enough, they shouldn't need it anyway. I'm trying to avoid serving giant images.
I know you can adjust maxium upload and I have this set to 6 mb as that's what I figure most phones at stock settings will take, but that's still pretty large. I can't tell users to reduce it as it will just confuse older people and younger ones will just stay screw it and head to facebook.
Alternative, it would be awesome if you developed OR partnered/integrated with a another service (smushit, kracken, short pixel etc) that would resize the originals and compress them...then we could still serve them larger images in light boxes without sending giant files sizes and hurting load times on mobile and SEO.