It sounds to me like all you are saying is that you want adventures that fit all PCs. As others have pointed out, you can do this in the existing level system just as well as you could in a point-buy system. At a certain point, some challenges (requiring flight, divination, etc) will be beyond characters of a certain level or point value, and so some adventures will by necessity be put into a "niche." Scaling adventures can broaden the niche, but it exists nonetheless.
The Dungeon adventure paths are pretty good examples of how to broaden the niche within a level-based system. The adventures come with "Scaling the Adventure" sidebars, and there are conversion notes for placing the adventure within a particular setting (Eberron, Greyhawk, FR, etc).
The Dungeon adventure paths are pretty good examples of how to broaden the niche within a level-based system. The adventures come with "Scaling the Adventure" sidebars, and there are conversion notes for placing the adventure within a particular setting (Eberron, Greyhawk, FR, etc).