Left shoulder under chin

With Driver and long shafted clubs:
Noticing the difference between the players on the regular tour and Champions tour, I saw many older players not getting their left shoulder down under the chin but rather stopping short of the chin or right at it level.
Watching the guys on the regular tour, they were turning the left shoulder down under and past their chin. It was not a dip but definitely a downward motion on backswing; on forward swing their right shoulder turned down and under.
Opinions on this? Is it a matter of flexibility, Pivot, etc.?

In general terms, could it be an evolution of the swing instruction from one generation to the next? The older player using techniques from their generation, and the modern player using "newer" mechanics. The "level" shoulder being more of an upright or two plane 70s ideal vs. a more rotational swing around a more angled spine which moves the left shoulder down.

On another point, I’ve noticed several of the new young guns are back to a severe reverse C finish, which was all but abandoned in favor of an upright, facing the target finish, allegedly because the reverse C was causing back injuries in the long term.