Your argument is a layman can't puzzle out JSON easily, but do you think hjson is any better? Syntactically it's core seems to just be QOL improvements over writing JSON by hand. It isn't any more intuitive from my perspective. In fact, in many cases it seems less intuitive by offering a greater number of ways to do the same thing.
I know right? That 85M is a real drain on my 16GB of memory on my macbook, amirite? What year are we living in when people nitpick over native performance. Is vim too heavy because pathogen takes ten fractions of a second to load more than pine?
The issue with their claim, I believe, is that the software isn't really circumventing any protections in place. It is simply using the existing publicly facing API. If the software made clear attempts to prevent this API from detecting or locking it out, then that would be an absolute violation, but I don't believe pulling crypto keys and reimplementing the API after REing it is necessarily a DMCA violation. Certainly it violates some other things, considering it is difficult to prove a clean-room situation when it was all done by one person. Seriously though, Snapchat should be focusing on hardening their API rather than trying to shut down imposter APIs.
While this does technically violate 17 U.S.C. section 1201 (a)(1) according to other case law, I feel the responsibility is upon Snapchat, Inc. to make sufficient attempts to prevent such subversion. RE is always a sticky area, and because it appears you needed to pull some form of cryptographic keys out of that process, you are likely in an unenforceable region of a DMCA violation.