I also feel that making me self-diagnose with a disorder would be very useful for keeping me small and powerless

That’s a valid way to feel, but for many people on the spectrum it’s the exact opposite. A diagnosis is an answer for why in NT spaces we often feel constantly misunderstood and out of place, and reassurance that we aren’t the only people like ourselves in the world. It’s also an amazing way to connect with others for tips on how to manage symptoms or other issues; if I wasn’t connected to other autistic people I never would have discovered there are tools to reduce my sensory problems, or found the ability to advocate for myself and what I need rather than shutting up and feeling inadequate for needing help.

Yeah particularly with ADHD I feel like many diagnoses are really "incompatible with wageslaving for 40 hours a week" rather than a condition that would, in a vacuum, affect the patient's quality of life.

Of course many ADHD patients do have real issues with their quality of life even outside of societal obligations (read: work, studies) in the form of e.g. not getting chores done, but as a former "problem child" who nearly had this forced on him back in the day, I firmly believe that there's a lot of pressure from the school system to get kids on meds just so they'll sit pretty in class even though the real problem lies in the system.