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.
This effect is visible when landing on dry bush strips, or in ultra-low flying by the reckless aviator, when a continuous cloud of dust is raised by the aerodynamic "squeezing" or "cushioning" between wing and ground.
To my straightforward (simple?) engineer's mind, it seems blindingly obvious that total lift is a variable combination of pressure-distribution and downwash effects, based on distant memories of fluid mechanics lectures and lab work. This "controversy" about the components of lift all seems a bit artificial to me, due to the apparent tendency to polarise opinions in an "all or nothing" approach. In other words, I think both sides are right, to some degree!