If downwash does not provide a significant contribution to total lift in straight and level flight, how do the deniers of this explain the well-established phenomenon of ground effect? This "floating" tendency which extends the landing run unless pilot input counters it, can only be caused by the downwards-moving mass of air below the wings coming into contact with terra firma.
Because when you come into ground effect the wingtip vortices are being reduced because there is no more air below to let them propagate, therefore drag reduces, hence the floating of the aircraft.
If lift would be caused by downward deflection of the air, why would there be wingtip vortices