This is intriguing stuff and as a long time "superhero" fan, I've done a wee bit of thinking on powers and the lack thereof. I've had a personal project on the go off and on for the last few years cataloguing (on card files, as I find it quicker and easier than using a computer with which I'm not very good),obscure "superheroes". Now, I realise one person's obscure is anothers "got the t-shirt" and to many of you folk, you'll be familiar with lots of my list, but, I started to think about the term superhero and came to the conclusion, as someone above says, that these are larger than life characters, in comics, pulps, books and story papers, dressed wierdly and fighting crime. Nowadays I use the terms:- superhero, masked and/or costumed hero, mystery man.
I agree with the point about non-powered heroes fighting gangsters and back street criminals, and succeeding, but how would Batman, Green Arrow, Catman(American or Australian), The Phantom manage against the might of nazi Germany or Japan during the war? Even though some of them succeed in the comics, it's not really very likely in reality. And that very point makes me realise that we are all reading comic books with very little based on real life. I can't speak for recent comics as I hardly ever see them.
I read for diversion and because I love the idea of masked, costumed heroes, super powered or not.
I don't like kid sidekicks and for the most part think they are a waste of space, although, as with Doctor Who assistants, they can serve an explanatory purpose.
As for the Tarzan thing, can we not just agree that he is an adventurer, rather than a costumed hero? Same with Sherlock holmes, Dixon Hawke, Doc Savage. No super suits, masks or secret identities.