I'm not against private diagnosis.
Shared care and shared titration with the NHS are not something NHS GPs have to accept, and whether shared titration is accepted or whether its entirely funded privately there are still guidelines that have to be followed to ensure that medication is prescribed safely.
I do think both ADHD and autism are underdiagnosed. I have an NHS autism diagnosis, but I don't have anything against people who seek a private diagnosis. I don't think their struggles are any less valid than mine. To claim any sort of benefit they would have to have substantial evidence to prove each of their struggles so I don't think people who have a private diagnosis are taking from the general public either.
I also think that private diagnosis for ADHD, especially for women is very beneficial. For a very long time neurodivergence in women has been ignored, misunderstood and misrepresented. Private diagnosis often offers follow up care options that NHS diagnoses do not.
I think it's wonderful that people are more in tune with their needs and mental health and a huge benefit is recognising that they may need reasonable adjustments at workplaces or in other professional settings.
As other PPs have mentioned, ADHD and autism are not learning disabilities. They're neurodevelopmental disorders. This means it doesn't impact anybodies intelligence however the way their brain works will impact how they access resources to education or their learning styles. This means saying that they need to accept they're "a bit thick" is offensive. It's not meant in any other way. It's meant to be inflammatory, and it shows your privileged position to have received an NHS diagnosis.
It's also important to note that ADHD has many presentations, typically inattentive, hyperactive and combination. Each presentation by definition will present differently. Some people outwardly show their struggles, some people internalise their struggles and some present in both ways.
I do think that in some cases of NHS diagnosis this is actually overlooked. It's very similar to holding women to male autistic standards and you're not always fortunate enough to have an assessor who understands masking plays a huge part for women, just the same as you're not always likely to have an assessor who doesn't have a rigid idea that ADHD isn't always physically flitting from one thing to the next leaving a streak of chaos as you go, but is a huge disorganisation of the mind instead.