What do experts mean when they say that teams are a means, not an end?
An end is a goal. A means is a way of achieving a goal. Therefore, what the experts mean is that teams are a way of achieving a goal, not a goal in themselves. This is important in business because it means that managers should focus on achieving the goal (better efficiency, more profit), not on trying to create teams.
It is possible for managers to forget this. They sometimes come to think that creating teams is important for its own sake. But team-building is only important for the impact that it has on the efficiency and profitability of the firm. If managers forget this, they may try to build teams even in situations where teams are not the best way to achieve the firm's main goal.
The meaning of this, then, is that a team is only valuable to the extent that it helps to achieve the real goal of a company.