The angle the shaft is on to start the downswing has a massive impact on contact, flight line and ball curve. The golf ball will typically start on or near where the clubface is pointed. Depending on speed the clubface will have about 85% of the reason for the starting direction of the ball. The path the club travels will add no or for many of us side spin.
Most players in the US have the club to flat at the beginning of the swing, steep at the top and then try to make corrections on the .25 second downswing. To be perfect set the club with the left arm parallel to the ground on the back and downswing with the club shaft pointing at the target line.
All tour players are good at this. These two videos will help explain the importance of the shaft plane.
https://www.youtube.com/watch?v=WvRgS1RAt90
https://www.youtube.com/watch?v=K29P6D2nAk4
https://blog.trackmangolf.com/swing-plane/
Trackman data on shaft plane.
Jim Hartnett, PGA