I see it quite differently, the leader is the single biggest influencer on the performance of the group. There are many examples in sports where just changing the coach has changed the team from an underperforming team to a leading team. Similarly with companies, a leadership change has often lead to a significant change in performance.

To understand that you have to understand that pack behavior tends to mimic the leader, so if the leader does X, then their reports do X, and the people who report to the reports do X. In large organizations you may find pockets where someone in the change decided not to do X and then everyone below them is free of that expectation (for better or worse).