One key criticism with PMBOK is it indirectly provides an image of the project manager as a superman/superwoman. This may be the case for construction projects (PMBOKs origins is in the construction industry) but for business type projects such as projects with IT based solutions our experience is that the functional and/or financial authority to make key decisions is actually with senior management and not the project manager.
Project managers also need advice and guidance from senior management and it is them that are best placed to make the key decisions. In PRINCE2 the responsibility for the project is with senior management both customer and supplier. But this does not mean that Senior Management need to get involved in a project on a day to day basis, as PRINCE2 makes use of management by exception tools.
One key criticism of PRINCE2 is that it misses the importance of the soft skills needed by a project manager and is light in the knowledge areas such as scope management & contract management and others which PMBOK provides guidance on.
The recent spread of PRINCE2 across the world (and there are predictions PRINCE2 will easily surpass the number of PMBOK qualified people within the next few years), is because PRINCE2 provides a SINGLE STANDARD APPROACH for the management of a project, whereas PMBOK gives each project manager the freedom to decide on their approach. Many government and global organizations have preference for a single standard approach to be used for all their projects and are adopting PRINCE2 as a result. The other advantage is that people with limited experience can use PRINCE2 whereas PMBOK requires a level of experience to apply its knowledge areas appropriately.
In summary, in addition to other required competencies a skilled project manager is one that has the ability to apply the guidance of PMBOK with the assistance of PRINCE2. A highly skilled project manager also has the know how to apply PMBOK & PRINCE2 appropriate to the risk, complexity and nature of the project but can also adapt it for those fast moving projects. Development of this competency comes with experience.