That's a really stupid take.
A diagnosis is very important because almost all mental/personality/executive functioning disorders share similar symptoms (anxiety, depression, etc.), but require different approaches for treatment.
It's very possible for someone to be diagnosed with ADHD and depression when really they're bipolar 2, and common depression medications (SSRIs) can have extremely adverse reactions with bipolar disorder.
It's also super common for women to not be diagnosed with autism, but instead be given a laundry list of other diagnoses instead.
A proper diagnosis is imperative to getting the right treatment, whether that's meds, therapy, or self help.