My take on this is that the classical mistake that people make here is exactly what you are saying. Typically the current business process is utilised as a point of departure. How wrong can one go?

In value chains or value streams one should always question the reason for existence of a business relative to the particular value streams within which it should participate, not only the ones it always has, or the ones it would like to. Once one understands what value streams it should participate in one derives the real reason for existence of that business. It could be vastly different from what the organisation currently represents. The business' reason for existence equates to the reason why the other participants in the value stream are prepared to tolerate the organisation, and pay it to deliver some value to the value stream, and not pay somebody else's business.

This provides one with strategic context. If you are in control of that one needs to accurately derive the new processes of the organisation that this 'new' strategic context implies. Typically one could end up here with a totally or slighly different permutation of processes than those that the original organisation believed it should have. In this exercise one has to ensure that these new processes, which will require a new permutation of resources to execute, directly enable the strategy of the business. Hence, a strategically aligned organisation within the context of the correct value stream.