You answered yourself in you last lines. Meds only make things worse, and carbs and sugar diet is the BOMB. I know is a lot of work but diet is key , do the best you can, also start seeing a Dr. who treats autism as soon as possible so he can guide into healing his body naturally which starts with the GUT. Lots of bacteria, viruses, candida etc cause all of those erratic behaviors. Diet, Dr to help you and off meds gradually that is the key. There are so many other natural supplements that you can use instead of prozac, for example Ashagwanda is being so great for improving behaviors. Get out of the conventional medicine wagon and take the natural approach or there is not hope for peace for anybody. Hugs.!

My advice, do some investigating, find out what is triggering his anger, document it. My son went through this stage, he used to hurt me too.
I figured out a way to communicate with him. I also showed him videos of what happened when people hurt other people, example, the people they hurt could end up in the hospital, and the repurcussions like jail.
So, for him, it stemmed from him not liking himself, being frustrated with his challenges/deficits, kids being mean at school, no friends, being a loner, hormones. Don’t let his anger, make you feel helpless or afraid, where it’s easier to just let him act out. Communicate with him that he has to help you find a way to make things better. Have you ever asked him what he wants, what would make him happy? How is with understanding what is real and not? If he has a hard time communicating, have him draw pictures. You may want to get something for him, like a punching bag, or another athletic outlet for him to release his frustrations.

His dose May be to high.

My son is 14 and is struggling with all the same issues. Which means that our entire household is struggling. He sleeps 10-12 hours a day and wakes up so hyper and it lasts for hours. He talks LOUD and fast. He talks about everything like he is an expert, even if he has no idea about what he is saying. He isn't trying to be rude, and he doesn't realize how loud he is. I have recently weaned him off of his mood stabilizer medication because it made him super angry and rude. I thought that was his O.D.D. but it was the medication. So I would rather take happy hyper than the anger. BUT I am hoping it gets better with time. Guanfacine made him suicidal to the point he was in patient for months.
He is also into everything. But so far nothing of value, and we have been able to fix most things.
He refuses to go to school on time. Partially due to being so tired. Mostly due to not liking his first few classes so he just avoids. No discipline or consequences seem to help for us either. We have school rules and family rules with rewards and consequences. He loses one minute of computer time for each minute of missed school. He tried to argue that for about a week, but now he accepts it without any anger.
He refuses to go out with us as a family on most outings. I used to feel bad about it, but now I have decided to accept it. Plus, we enjoy a little time away without him. Sad, but true when he is having difficulty regulating his mood.
I don't have any good answers, but I have tried all the things you have mentioned as well. (minus horse therapy) It is so nice to know I am not alone, that just maybe it is the ASD and not me. My goal is to try to help him feel heard when he talks. I want to try diet and natural remedies because medication side effects are not worth it. But I will keep him on his ADD meds. He hates trying herbal things, he hates therapy. He only eats pizza. So I have my work cut out for me.
I was able to get him to do cbd oil for two days. It really helped his anxiety. The drops worked in moments. Maybe you can try that?

if the diet seems too much, try to do a round of parasite/bacteria killing, that is something you can do for just a certain period of time, you need help from a holistic/ autism Dr. to suggest right products and most important how to detox since after killing pathogens the body gets burdened and needs help to detox or behavior gets crazy crazy.