An essential element of lean manufacturing is a level loading of demand - or at least reasonably level. Toyota uses pricing to accomplish this.
It is becoming more and more apparent that lean is a company wide issue and that giving any department or function an exemption leads to failure.
I agree. The company needs to be viewed as one interdependent system not independent departments. The system needs to be optimized as a whole. And that means optimizing the overall system not optimizing the individual departments independently.
World class management understands this concept. But so many of our current management practices undermine attempts to optimize the overall system: rating and ranking people, accounting systems, performance goals, focus on quarterly profits, etc. Some have difficulty understanding that optimizing individual components of a system is not the best strategy to optimize the overall system but that is the truth.
Book, online articles and web links on systems thinking