There's no question that the pros have got way, way, way more lag in their swings than most amateurs. Show me a pro who doesn't have at least 90 degrees of angle between the arm and the club when the left arm is parallel to the ground on the downswing. Almost no medium to high handicappers achieve that. And of course, all the tour's longer hitters have much more lag even than that. So it's absolutely ridiculous to say that you can get (big time) distance without lag. The more cogent question is, how do you get lag like that? And more importantly, how can poor ballstrikers or short hitters
learn
to get that lag? Most instructors understand how to get lag but have trouble training students on how to do it. It might be because they are athletic, and underestimate the athleticism and coordination of their students.
Also, no decent ballstriking pro ever flips his hands or loses his right wrist angle at any point during the swing. Maybe sometimes when they really get the club stuck behind them they do a little flip, but if they did that and you saw a still image of their swing just after impact, it would still look nothing like the flipping that a poor playing amateur does.
Most good ballstriking pros, 45 degrees of swing arc or more after impact, still have their left arm straight, left wrist flat, and their club shaft parallel to their left arm. Almost no amateurs can do that; their club will have swung past the angle of their arm, usually by a lot, and their left wrist is no longer flat. IMO that, more than anything else, is the secret to long hitters' distance.
I think it means that, first of all, they started with lots of lag on the downswing, and second of all, they kept their hips moving forward and turning, and their shoulders turning all the way to the finish of the swing, the club always being towed behind.
Maybe one mental image a person can have to help lag and distance is to think of the maximum extension of the swing being well after impact, maybe 20-30 degrees after impact. That would keep the club acclerating through the impact zone, and might help get rid of some of the flipping.