By fixing the underlying conditions that lead to the behaviour classified as ADHD rather than depending on stimulants as a(n admittedly very effective) crutch to power through them.
From what I understand, ADHD is typically thought to be the result of an inefficient (outside of an accepted typical range) reward/reinforcement system in the brain - whether due to not producing enough of the relevant neurotransmitters, or not being "sensitive" enough to them (yes, this is oversimplified).
How would MDMA (or any drug) alter this? Stimulants used to treat ADHD typically work by either getting you to produce more of those neurotransmitters or getting them to stick around for longer by inhibiting reuptake. I'm not sure of any drug or treatment that could permanently change these things in the brain.
I think the idea is that neurodivergent people tend to have a lot of really damaging, highly ingrained thought patterns as a result of their time before being properly treated. Unwinding some of those might make you more effective both with and without medication -- although that's not to say medication would not continue to be useful.
ADHD is primarily a hardware problem. Unless MDMA can fundamentally change how nerves handle neurotransmitters, the effect is going to be temporary at best.
