I think both things can be true. Large entities, no matter private or public, suffer from inefficiency. But, private entities have more control over the allocation of their resources.

With a private enterprise, you have stakeholders at the top that can single-handedly reallocate resources to/away from endeavors as needed. Within government, that can be a lot more difficult as resource allocation is more complex with many more stakeholders and layers of bureaucracy. This is especially true in democracies where changes have to be approved by either the citizens or partisan groups within congress whose goals may be in direct contradiction to the success of your organization.