Originally Posted by
Myskin
Because at one point, for a variety of reasons, the concept of legacy had become particularly important in the DCU. They saw that they could create a lot of good stories which revolved around it - and in fact, a TONS of good and sometimes exceptionally good stories were created about it - and legacy had become a thing within the DCU.
That's the whole point. Superman is not the only factor which should be taken into account when you deal with a whole narrative universe. If writers want to sweep the whole concept under the rug, fine, but at that point they will have to deal with a simplified DCU and - if they don't replace the concept of legacy with something which is just as important - the narrative world they will deal with will be simply impoverished. That's exactly what happened in the New52.
You are overestimating the importance of Superman as the first superhero (and even the most physically powerful one, quite frankly). There inner factors and outer factors to make a character relevant. The inner factors concern the depiction of the character, the complexity, the world he/she lives in. The outer factors are independent from the creative force behind the character. Superman being the first superhero IMHO is simply a outer factor. It doesn't make him more important than him being a Lord, or a blue blood.
By the way, now that I think about that, I really can't remember relevant stories about Superman being the first superhero and the most "inspirational" one. I mean, there isn't any major superhero who was inspired by Superman. Batman, Wonder Woman, GL, and so on, decided to become superheroes because of individual choices. Of course, Superman has his own super-family, but every superhero has a bat-family, or a WW-family. Quite frankly, the only exception which comes to my mind is the Legion of Superheroes. But a lot of superheroes created individual supergroups, too.
I think that the overemphasizing the importance of Supes as the first superhero is just a way to balance the inferiority complex the character has developed towards other, better developed character. Let's take Batman. Batman was never the first superhero (well, until the New52 I think). But in the latest 3 decades he has been so well-developed, so interesting, and his universe is so rich and full of characters that the date he debuted in is completely irrelevant. I am 100% sure that, if Superman was in the same situation of Batman right now, him being the first superhero wouldn't be such a big issue.
There are character who are superfluous, and character who are so interesting and well developed that getting rid of them would be simply silly. Some of these characters are based on the concept of legacy.
I repeat it. As far as I remember, nobody really made a big issue of Jade being older than she appears to be.