Curious, what do you mean by larger "sweet spot?" I find that crop sensors have MUCH larger sweet spots than full frame, because the lenses aren't pushed as hard since only the center of the image circle is used. A wide angle crop will almost always be sharper and brighter edge-to-edge, given the same field of view. Same for telephotos too, except edge sharpness isn't as important for most applications. I think that legacy lenses are holding FF back.

In my opinion, a better sensor in a smaller format is the future as far as image quality AND cost effectiveness goes; FF isn't going anywhere, but crop sensor technology will only get better - and it's pretty good already!