I agree... to a certain degree. I don't think every sort of gatekeeping makes you an asshole, but this... does apply, unfortunately.

The specific reason for my take here is that people dismiss things they don't understand all the damn time, especially if it's an "invisible" affliction. Implicitly and sometimes without even realizing it has happened.

It is impossible for people to understand major depression, "significant" ADHD, etc if they haven't experienced it themselves, and most people just haven't, and therefore can't. While that is true, the brain is only too eager to pattern match, which is where you get into "major depression is like when I felt slightly sad once and could just focus on something else" and "ADHD is just like when I didn't particularly feel like doing that one thing, but then it took almost no additional effort to do it anyway and it made me feel better afterwards". If you try to map those experiences onto people with, bluntly speaking, any kind of actual problem at all, you will think the problem is much simpler than it realistically is to anyone actually affected - and not even realize it is happening.

Some people can get closer to actual understanding through (near) connections who both suffer obviously enough and are talkative enough about it - but this is rare and it fucking shows.

In short, it is intellectual laziness proper, in a form that you very definitely can do something about. As opposed to just saying "you and you with your definitive respective neurodevelopmental differences from the average, you should be able to tackle any consequence arising from it with straight up aplomb". Which, in case it wasn't obvious, I'm not a huge fan of.