Not only is there this vast difference in annual invested time, but 80% of the directors would not have a background in the company or industry on whose board they serve. To be sure, they have been chosen for individual attributes such as a glowing track record of achievement at the head of some organization but most often they are not chosen for company/industry knowledge.
In addition, directors are usually involved in many other activities from a second or a third board to their own investments and recreational interests let alone children and grandchildren.