You make some good points, and I don't argue with any of them (although, per your last point, I've found that eating something salty helps me from time to time :) ).
I guess my main issue is if we ignore diet as a cause, then we quickly get to medications, which can make the situation worse (not necessarily make the problem worse, but other problems can arise as a result).
I think that if psychiatrists were as well trained in food chemistry as they are in drug chemistry that the world would be a better place.
Finally, one personal anecdote - my business partner is really attuned to my moods. When I come into the office in a grouchy mood (of which I'm often not aware), he'll call it out. The first year or so it was off-putting, and somewhat annoying, but after I got into Keto, I noticed that my mood was changing as a result of the food I ate the day(s) before. Over time, our whole team has started to become attuned to it as well (yeah, it's kinda weird, and no, we are not all on keto - we tend to have fairly varied diets among us). The great result is that we call it out like, - "you're in a grouchy mood, what did you eat yesterday?", or "I'm not focused today" and the other person asks what they ate recently. This has been really effective for us, because most of the time it's the food affecting us, as opposed to us just being a jerk. Obviously other things weigh too, such as other stressors in life. but many little things we can trace back to food, and it has made our team much better at working together because we are freer at calling these sorts of things out.