The video game prescribed by doctors to treat ADHD

But that's exactly my point. We know that "Malaria" exists because we can point to a parasite that causes predictable symptoms. We know that there's something called "COVID-19" because a virus exists that we call "SARS-COV-2" whose presence we can test for. But there isn't any parasite or molecule or virus or bacterium or lesion that "causes" "ADHD", because "ADHD" is just a result of how our brains came together, not a real on-off condition that someone can have due to a cause like "Down's Syndrome". You cannot arrange real conditions on a spectrum; they are binary. Either you have them, or you don't. When you start measuring arbitrary "degrees" of a "condition", you're just assigning parameters to naturally occurring results based on variations in biology.

Using the same logical premise that allows for "ADHD" to exist, I can make up any amount of "conditions" that someone can be diagnosed with. I can diagnose people with Tonal Mismeasurement Disorder (people with bad intonation), Height Growth Disorder (short people), Hand-Eye Coordination Disorder (people who aren't good at precision sports), etc. etc. But these aren't "disorders" or "conditions", they're just arbitrary labels slapped on people who are less able to perform a certain human-invented task due to their genes and how they were raised.

The fact that you and I can focus better if we take amphetamines doesn't prove that ADHD "exists". We accept that some people are naturally stronger than others; well, naturally weaker people could take anabolic steroids in order to catch up to naturally stronger people. Does that mean that "Strength Deficit Disorder" exists?

When you talk about how an inability to focus has caused you difficulty, what you're Actually observing is that the economy, school systems, and bureaucracies have been set up by people that have a relative surplus of focus and determination, and this method of organizing society disadvantages you. It's as if the economy was set up by people who made every transaction hinge on how much you could lift unassisted, and you and I are naturally weak people. The fact that drugs help us perform better doesn't mean that "Strength Deficit Disorder" is real, it just means that our relative shortcomings can be remediated by using certain chemical cocktails.

I understand that the dopamine shortage and metabolic effects can be measured, but they're not sure ways to prove that someone has attention problems. For every "ADHD" person who has less dopamine, there's someone on the other side of the spectrum who has more dopamine. It's not as if ADHD people are uniquely lacking dopamine and the majority of people have "normal" levels. When you take amphetamines, you're experiencing what a 50th-25th percentile person experiences when they focus on something. You're not experiencing the other side of the bell curve, what I called "ASRB" experience, which is unparalleled clarity of mind and memory.

I am more amenable to something like your "legally blind" example. If we called it "legally focus-impaired", that would reveal the fact that we're selecting arbitrary definitions based on a spectrum of performance.