I think as a general rule you should avoid doing something that will create work for those assessing your application. They already have dozens of applications to read through - all with proposals, statements of purpose, and written work. I cannot imagine that they would be happy to receive a 21,000 word thesis, especially when they have stated that brevity would be considered desirable. Instead of submitting the whole thing and expecting them to pick out the bits that they 'want' to read, it would be a much better idea for you to do this yourself and submit one or two much shorter pieces (of roughly 2,000 each) which you think best exemplifies the work you have done.
Good luck with your application. (up)