My experience has been somewhat similar to the above - my teenager most likely has ADHD and/or ASD and we have really struggled to access any assessment or support. The GP was great, but the NHS waiting lists for CAHMS were so long that they said there was no value in joining it as she would be an adult by the time she was assessed and would therefore no longer be eligible. We therefore had no choice but to go privately - even here the waiting lists were long but she did get to see someone in the end and is now in the process of doing the various evaluations to work out what the diagnosis, if any, may be.
In her case, the challenges she has faced have led to additional mental health challenges, and while we know that labels aren't always helpful, both she and I feel that it would be hugely helpful to have the "label" if she is indeed neurodivergent, to help make sense of why she feels different and why some things are so much more challenging for her, as well as hopefully helping us identify strategies to help her.
So yes, this is a massive issue!