From everything I've seen, 'Blade Runner' is his biggest baby of them all. I doubt he's made two Director's Cuts, over a decade apart, for any of his other films. And the fact that he's coming back to do an 'Alien' prequel, or at least something within the same universe... and pretty much right after Cameron came out with Avatar... also, I think you're being a bit Ti nitpicky here: when I said "greatest sci-fi director of all time competition", it didn't mean that he only directs sci-fi, it was a credit to the fact that he has directed two of the greatest sci-fi movies of all time, films which would probably find themselves on almost any top 5 list of sci-fi films. When you directed 40% of the top 5 sci-fi films of all time, you probably qualify as one of the greatest sci-fi directors of all time.
Well, while I appreciate the gift (as related as the two genres are, 'Legend' is a fantasy film), my take is different: 'Blade Runner' and 'Alien' have got to be among his best, if not certainly his best, work, and the fact that those three films are what essentially launched his career, imo, means that they are just that much more
important. In fact, part of my original point is that it's interesting that he's coming back
to sci-fi after all this time off, so, not only had I already acknowledged the fact that he's been doing a lot of non-sci-fi work for a long time, the fact that he's coming back to the genre is part
of my thesis why this all might have something to do with Cameron.