Suction on the top is not even half of the lift force being generated. Most of it is from the air hitting the bottom of the wing and deflecting downward. Air has mass, so if you throw it downward then by Newton's second law (F=ma) there has to be a reaction upward by the wing. As a thought experiment, imagine trying to hold a piece of plywood in the air as you go fast. It will lift like nobody's business. At about 40 mph or so you won't be able to hold it down. There will be some lift from the topside due to air trying to get over the top and meet up at the back, but most of it is from air hitting the bottom side and being thrown down. Downwash is the same thing, air that made it around the wing at an accelerated speed due to venturi effect, getting thrown downward behind the wing. Both forces contribute to lift (Newton and Bernoulli) although it is inaccurate to say they simply add up. It's also way off to say the topside of the wing is the only place where lift is created. Circulation is the total picture, lift is created from air circulation around the wing. Here's a pretty good link explaining circulation.