Hello, fellow parent here. My daughter is two with a different genetic retinal disorder. She was diagnosed when she was 6 months old, so I can certainly relate to what you are going through. I remember those weeks of feeling "devastated and destroyed" and feeling helpless. I am here to tell you it gets better. I had to go through a grieving process for the life I imagined my daughter would have, but didn't even realize that I had in my head. Focus on what you can do.
First, absolutely get a different retinal specialist and/or ophthalmologist. You absolutely want someone who has a better bedside manner and will answer any questions that you might have.
My family is involved with the
$1 which funds research for inherited retinal conditions. You should be able to contact a local chapter and be put in touch with other families with the same condition and get information on the latest treatment or gene therapies.
Even if there is no treatment currently that doesn't mean there won't be one in the future. That said, you also need to prepare him for the world currently. You should contact your school district so they can begin providing services for his visual impairment. He might not meet the legal definition of "legally blind" currently, but he might in the future so he should qualify for services.
Please feel free to PM me if you need any more information, or just someone to talk to.