Finding Reliable Help
“Who can best diagnose ADHD—psychiatrists, psychologists, or therapists?”
Any mental health professional can diagnose ADHD if he or she follows the guidelines and criteria. Some are more experienced than others. A psychiatrist is the physician with the most experience with ADHD and medications to treat ADHD.
If your psychiatrist is yielding to you and what you learn to determine medication, I would suggest seeing someone else. This does suggest less knowledge than you want with the professional treating you.