The manager's role is much more important in an actively managed fund than in an index fund. Index funds have consistently outperformed actively managed funds in recent years, and they don't hire managers to be stock pickers. Therefore, experience does not make a huge difference in this type of fund. But in an actively managed fund, a manager is expected to pick stocks and to time their sales and purchases in an advantageous way for shareholders.
Experience is a very valuable attribute for such a manager.
Investing almost always requires living through some disappointing times. I'm not thinking about the manager staying the course - he or she gets paid to do that. I'm thinking about whether you will stay the course. A new manager may be full of energy and ideas. But an old-timer is more likely to win and keep your trust when times get tough.