Copilot's corpus is quite literally tomes of copyrighted work that are encoded and compressed in its neural network, from which it launders that work to create similar works. Copilot itself, the neutral network, is that corpus of encoded and compressed information, you can't separate the two. Copilot stores and distributes that work without any input from rightsholders, and it does it for profit.

A better analogy would be between a browser and a file server filled with copyrighted movies whose operator charges $10/mo for access. The browser is just a browser in this analogy, where the file server is the corpus that forms Copilot itself.