You can pretend that clinical significance is the gold standard measure of disability if you like, but you should recognize that you leave a MASSIVE gap in your effectiveness both as a diagnostician and a practitioner if you neglect all the masking your client has been doing to deal with everybody's demands their whole life. Seeing that bias in someone pretending to treat me would be enough reason for me to walk out of the appointment and schedule with someone more capable and knowledgeable.

Yeah, my guess is that this post is implying the typical case - it wasn't disrupting grades specifically, so it wasn't diagnosed. You may have gotten those grades by staying up until 3am as a child, lying to get out of forgotten homework, had more injuries, pushed through work by building up a healthy reserve of depression and anxiety, struggled socially because you couldn't prioritize both school and socials or because you couldn't connect with most other people because of your way of talking, been horribly forgetful, etc. but because grades number stays high, nothing is wrong. It's easy for people to see grades as the metric for mental wellness which is wild