Indeed dbcontext is redundant with the DocbookInContext macros that allow to produce DVI or PDF output by translating on the fly the DocBook tags to ConTeXt macros.
It is not the same process, and dbcontext have the following advantages:
no ConTeXt file must be written to include the XML file,
figure conversion is supported,
the intermediate context file can be kept,
layout customization should be easier.