After it heals, you should try some of this. It works wonders in hair regrowth, my gelding had a scar as bad as the mare you gave us as an example. Two days of this stuff, and the scar was covered in fur:
You will always have those that post negativity. There's no way I would've called a vet on that. It's looking great and healing fast! I actually just use coconut oil on wounds. It's an antibacterial and antifungal as well as speeds up collagen production. I use it topically and give it orally as it reduces inflammation.
It amazes me the ways I have seen horses torn up and how well most heal. My dad use to have some stuff that looked a lot like this and it too worked miracles. The injury looks great and has healed amazing.