Well, I don't think he is doing an absolutely amazing job if your horse has flares. There really isn't a reason for flares to develop between trims unless the trims are too far apart. A mustang roll doesn't automatically mean no flares. Two different things.
So, the next time your "amazing farrier" comes out, look critically at the finished work. Are there flares? Even a little? If not, and you see flares before the farrier comes out the next time, your horse may need to be trimmed more often and/or possibly more agressively. I vote for more often though until you are content with the hooves.
Also, take before and after pictures. It's amazing what you can see in pictures that you miss in real life.
Flares on their own won't make a horse lame. They do put stress on the hoof though and if allowed to progress you can end up with white line disease, chipping, cracking -- generally poor hooves which then can lead to lameness.