Been a week, so I’ll answer my own post, I found a partial solution. Mostly I do screen caps, so I take a screencap, then open it in GIMP and change the pixels per inch. In Gimp that’s Image > Scale Image, then change the x resolution and y resolution from 72 to one much higher, 220×220 seems to work. Scale the image. It won’t change size. Do not crop it yet, or WordPress will undo that on crunching (don’t know how). Export it to .png, not .jpg
Then upload it to your media library and crop it down to the size you want and save it.
It isn’t perfect–it still shrinks the file–but the results seems much better. Still looking for a way to post images unchanged if anyonw knows one.