Like Preaching to the choir means to speak for or against something to people who already agree with one's opinions.

What is saying when an idealist, bookish inexperience, fresh-out-of-college employee/group of employees (like a department) is/are put on the helm (and given enough power) and they start to preach the experienced, practical, seasoned employee/group of employees (the other department) about te following:

1.) the ideal procedures and protocols that should be followed like obsession with standardization (even if these procedures are redundant to subject matters)
2.) Bring in ideas that are new and fresh for inexperienced but the organization (experienced Departments) have been tested and failed before.
3.) Bring in Over the top ideas that are simply laughable if exchanged in business circles but are given serious time of the day.

when they themselves lack experience of how the market, the industry or the world works.

Note: If you are thinking how could this be happening, this might occur in combination of nepotism, cronyism and/or in Laissez-faire or seagull management style

These inexperienced department who have power over the others departments but have zero experience with the other department's work flow, still just because they have been given power they preach the more wiser departments.