Good questions! Let's try to tackle them one by one...

Who are the most damaged by frequent flyer programs, out of the people who fly themselves?
I disagree with your statement that FF programs penalize low-volume customers. That's only true if, in the absence of FF programs, you would then benefit somehow.

If FF programs went away, would you suddenly:
- have priority in waitlists? No.
- be treated better during irrops? No.
- no longer get the back of the plane or the end of the queue? No.
- have a better chance at Upgrades? No. Upgrades would simply disappear.

I believe if FF programs went away the losers would be the loyal FF members. You as an occasional (disloyal?) flyer would not see any benefit.

Which major/flag carriers have reputation for good treatment of disloyal/occasional flyers?
Southwest
Midwest Express

Are there any people here who are able to pursue the policy to fly an airline just enough (with some safety margin) to earn and maintain the top elite status there, and fly the rest of their flights on other airlines so as to earn status there as well?
I'm sure here on FT you will find many people who have high status in multiple FF programs.