By the same logic paraplegics aren't disabled because they just aren't in an environment suitable for physically disabled people.

Not really, though. Rigid structure helps with ADHD, but only when someone else is enforcing the structure. Prepubescent kids with ADHD aren't typically capable of maintaining their own structure. They aren't neurotypical, it's more than distraction and energy, they have a functioning issue. They can't tune out all the stimulus that normal brains do, and because of it they miss a lot of social cues that help with development.

My son has ADHD and no amount of reorienting our family environment would help him - he could (and has) literally be in a bare concrete room with nothing but his thoughts and get distracted and slam his hands together making exploding/punching sounds for hours, where a typical kid would get bored in seconds.