I am not sure why, but if you convert your lines in the profile sketches to construction lines, then a Boundary-Surface will work. It should not be like that as the selection manager should produce the same results but it does not.
Also for some reason Loft or Boundary-Boss creates self-intersecting geometry.
However Boundary-Surface and Surface-Plane followed by Knit does produce the wing tip. I haven't tried Lofted Surface though.