Off the top of my head, a scimitar-shaped wing might impose a high torsion load on the attachment to the fuselage, in addition to the usual bending load. Thus the wing box would have to be heavier, and the extra weight might undo any advantages that the planform itself contributed.
Also, it is significant that scimitar-shapes are hitherto found on rotating components, the fluid speed over which varies with distance from the hub. LM has got it right. This doesn't apply of course to a wing.