@ant_pruitt have you ever tried https://saerasoft.com/caesium/ph/ or anything similar? I presume it just restructures the file so as to make it more compressible, but it still feels like it might be strong voodoo. I don’t create enough pictures that the extra space would matter to me, but someone like yourself probably wouldn’t mind smaller files if they really are indistinguishable from the originals.
Not this one, but there was another service similar to this that I didn’t find any use for. Photoshop can shrink jpgs for me if I need it to.