Here's Kevin: Kyle and Jamie have similar builds (about 5-foot-11, 165 pounds), and they do a lot of similar things in their golf swings. They both start by setting up to the ball to maximize distance. They have wide stances, their spines are tilted to the right, and their heads are well behind the ball. These address characteristics promote hitting up at the ball, which is essential to driving it a long way. Watch these two videos and then read my analysis below to learn how you can hit the ball farther as well.
Both players make a huge shoulder turn over a braced lower body. Notice how they allow their heads to move some. Restricting all head movement with a driver normally leads to power loss. Jamie simply allows his backswing to continue to gain extra power by continuing to hinge his wrists. This is a tremendous power source, and it requires flexible wrists. If he were playing on the PGA Tour he would likely shorten it to gain accuracy, but that's not the game he's currently playing.
Take note of how their downswings are triggered by leading with the lower body, technically before the club completes the backswing. As with many power-hitters, it's difficult to pinpoint exactly when the backswing ends and the downswing begins. This "two-way" helps increase the angle between the left arm and the shaft, amplifying their speed potential at impact.
Both players' bodies have unwound at extremely high speeds, and their heads are well behind the ball. Both players heads go down and back through
Kyle and Jamie continue to rotate their bodies hard and have the same unique arm action at this point. Their left elbows don't point downward as much as many players' arms do, almost giving them a "chicken wing" look. They likely developed this to prevent the clubface from closing and to prevent hooks. If you're a slicer, I would not suggest you copy this part of their swings.
Because the ball is long gone by the time you get to this point, it doesn't really influence the flight of the ball, but this is more a result of the things that happened prior....good or bad. You can't go wrong, however, copying their balanced finished positions, which are quite remarkable considering the speed at which they have just swung!