I know exactly what you are referring to patpending. I am also a Tmo HTC One user, and the drastic reduction in our MMS is pretty disgusting. There is usually a size reduction in an MMS, but the HTC One on Tmo is definitely drastic and extremely annoying and discouraging. I do not use facebook, and can not attest to any reduction with that program, but stock messaging on this phone on this carrier sucks. Maybe it is a Tmo thing, as opposed to an HTC thing, but why they, or anyone, would reduce the size this drastically seems to be a foolish move, on such a flagship device, in this day and age. The size reduction seems to vary from image to image, but each and every one I send gets reduced to an unbelievable size.
If you happen to find a fix, please let us know (I also have mine set to 1000k).
Actually I just sent an image of 11 kb, and it didn't compress it whatsoever. But when do we ever have the need to send a pic that small in size?