Ganges, I do know what the context part of the English course entails. You are right that it differs from normal Part 1&2 essays but the situation you described is only one of the options available to students.
You can do an expository piece, creative piece, persuasive piece etc and some people will base their response closely on the text while others will choose to delve into sources outsides their set texts.
Context is a very free area of study and I think personally that essays on themes, character developments etc can only help in any form of writing you choose to do. Eg. If you do a creative you still have to make references to ideas, themes in the text and a poor response will be one that does not embody at least one of the Context set texts in a response