One of the things that Wizards’ “fourth edition” of Dungeons & Dragons was meant to do is expand the “sweet spot”. It was felt that the experience of “third edition” in the middle of the characters’ careers was clearly superior to the experience at lower or higher levels. “Fourth edition” would reshape the lower and higher levels to play the same as this “sweet spot”.
I think, however, that one of the things that made D&D successful was the stages that the characters moved through. That the experience changed rather than staying the same. That’s exactly what kept many people playing D&D instead of many of the other later games.
And really, why bother with levels if you want this static experience game? For that matter, if you like the “sweet spot” of “third edition”, why not just play it and stay in that spot?
And if there were problems with the areas of “third edition” outside of the “sweet spot”, perhaps making them both unique and better would be a better fix than extending the “sweet spot”.