the Hatfield design view was that they would only improve a bad wing – "Hatfield does not design bad wings"
So Hatfield didn't design the Mosquito with its bad stall (according to Winkle Brown), or the Comet 1 with its ground stall, or the DH110 with its flutter, or the Trident which went through half a dozen wingtip designs in drag reduction attempts before the wings were finally clipped to preserve fatigue life?
Preserve us from designers' hubris.