You make good points all round. A well written post and I commend you for it.
I will say though, that this is a genre where reality and physics do not apply.. in comic books, people can fire laser beams from their eyes and men can lift tanks. So going beyond the boundaries can make sense in setting.. but those are the ones with super powers.
I guess with the more human heroes, it does apply when you're talking about full on physical confrontations.. in a battle against untrained or lightly trained thugs, someone like Catwoman or Spoiler can rightly take them down with ease. Combat is about technique, and many martial arts take advantage of the opponents strength and weight and turn it to their advantage. I do suppose in a confrontation vs trained opponents.. for example, Catwoman vs Nightwing, these factors would apply.
From a financial / comic publisher perspective its a bad move: he's a cash cow.
From a real world perspective? once it became apparent he was irredemable then the blood of everyone joker has and WILL kill is on batman's hands too. Sometimes you have to take the personal sacrifice for the greater good. Yes, its a line that comes with a price, but again: personal sacrifice for the greater good, and he is no more evil than any policeman that shoots a killer to protect people or soldier that kills to defend his country.