I think if it’s easier to say your son has autism, then that’s what you should say. When my sister had cancer, I didn’t say my sister is cancerous. I didn’t say she “is” cancer. I said she “has” cancer. (now “had” — past tense)
We use words too harshly sometimes, I think. Like when people say “I’m fat.” No, we’re not fat. We have fat. Sometimes more than we want, but we shouldn’t identify ourselves by the components we’re made of. We don’t say I’m bones, or I’m skin, you see?
In my eyes, your son HAS autism. And he’s beautiful. And so are you for working so hard to figure out the best way forward. :)