The rapid naming is visual identification, right? So these results indicate that basically anything that he has to process visually or with writing is notably slower than the tasks he can complete using only his aural-oral connection?

Which feels like it puts us back in the visual processing realm.

How would a dyspraxia/motor planning diagnosis affect his visual processing? Would this be an expected consequence of that type of diagnosis?

And yes, his spelling utterly falls apart when he has to use it in context. Even if he spells the word correctly orally before he writes it or has it written in front of him, he still frequently writes it wrong and erases multiple times. He even forgets spaces between words still.