"Gaited horse farriers," as a class, will always cut back the heel and allow the toe to grow out. This is because that reduces the efficiency of the stride, holds the front foot on the ground longer, and that front foot will come off the ground at breakover with more energy. That give a more "impressive" stride.
If you are going for blue ribbons you want that "impressive stride." If you are riding for pleasure you want maximized efficiency of stride. That means a trim to anatomical correctness (usually a short toe and a more heel for a "stood up" foot).
I've personally fought this battle with three farriers over the years. I've discharged two because they would not follow my instructions. One figured out he had been badly informed by his "expert consultant" and ended up doing a fine job for the three years he worked for us.
If your horse needs shoes to stay sound then shoe him. Boots might work, but if the horse is unsound under saddle why would he suddenly turn sound when at liberty? Boots are generally a Bad Idea for turned out horses.
Your vet is right about "guarding."