Interfaces designed deliberately to contain high density of content and actions

There has been a strong trend towards the simplification and shallow IA of modern websites and applications, yet I can't help but wonder if there is also some correction required for certain applications that have been oversimplified and as a result reduced its utility and usability for the user.

I am specifically referring to applications that require expert training and knowledge, and some examples include control systems for water or power plants, software to monitor and optimize mining operations, visualization and search tools for scientists, trading platforms for financial institutions, etc.

Has anyone out there worked on complex systems requiring the design of dense content and functions? Has the simplification of the original interface design resulted in a loss of 'user-friendliness' that was not expected?

I am interested any research or examples to would illustrate or highlight situations where complex interfaces are actual more beneficial.