I don't know about too much heel, could be brought down a bit more but to do that you'd have to start slicing away frog to bring that down artificially - doesn't that seem like we'd be forcing an unnatural shape on this hoof? Also are you talking about his new pictures in the newer thread, or the last ones from this thread?
And unfortunately no, grazing muzzle is not an option as he is not close by and I don't get to see him everyday - besides that I'd be worried about his GI health, since horses are supposed to have food constantly in their stomachs.
Heels need to be trimmed down to frog level to balance the foot and help the frog do what it's supposed to do.
Here is a IIIBarsV series. She is an accomplished barefoot trimmer. I learned most of what I know from her:
The heels can make or break the HPA (Hoof-pastern alignment). The heels grow forward on an angle. The longer the heels get, the further forward the weight-bearing position. Depending on conformation, some horses will either grow tall heels, or get crushed heels. Upright and club hooves are more prone to tall heels and get a broken-forward HPA. Slopey and long-pasterns/sickle hocks/camped under typ...es are more prone to underrun or crushed heels, which creates a broken-backward HPA.
Wisher has a nice in-between pastern angle normally, so she tends to stay in balance in terms of HPA, but still has underrun/tall heels and a slow breakover at the toe.
With heels untrimmed but flares removed, I have put her into a broken-forward HPA. If she had a shoe put on top of this, she would be considered short-shod.
Wisher models for a demonstration of how trimming or lack of trimming of the heels affected the amount of frog pressure the horse is able to get.
If the heels are left long, the horse is not only impacting the ground first and weighting the frog second (which puts the entirety of direct impact and concussion on the heels regardless of footing), but results in heel contraction, frog contraction, and altered landing.