so we can all pretty much agree that this is relatively painful for the horse....?
No way to say how much discomfort, if any, this horse may currently experience. Horses are remarkable in their ability to compensate and tolerate.
and is something that can be "treated" with corrective shoeing?
Not really. Corrective shoeing depends upon a definitive diagnosis. None available in this case. Is it DSLD? Maybe, but those horses will almost always load the heels, even with extreme drop (to nearly horizontal) in the fetlock angle. You indicated this horse stands/walks on it's toes. I've seen DSLD horses perform at moderate level and even carry/deliver a foal. In every case, they fully load the heels.
Again, this is a case better reviewed in person rather than via photographs. If DSLD, then elongated support (eggbar, fishtail, etc) is the standard protocol. It's NOT a cure... just prolongs the inevitable. There is no cure. If the problem is related DDFT then protocol could change. Some may recommend increasing elevation in a DSLD case (e.g. Dr. O'Grady). I disagree in that wedging the heels causes the fetlock angle to drop. More to the point, an increase in caudal elevation reduces strain on the DDFT but INCREASES stress on the lateral branches of the suspensories and the SFT.
If DDFT, then wedging could be appropriate. Fairly easy to test in either case but must be done in person.
Step one is proper diagnosis. Then we could discuss treatment protocols with better authority. Short of that diagnosis, we're just best-guessing a couple of photographs. I've never shod a photograph.