Have you? The size of the core Facebook application binaries disagree with your statement of “tens of thousands of classes don't directly translate to increased binary size - its usually the dependencies of the code that results in such large binary sizes”.
I'm simply "speculating" that a large number of reimplemented classes might not be the reason for the increased binary size from anecdotal experience of building similar app binaries for iOS.
FWIW, I think this comment gives a pretty good reason for why the binary size is large - https://news.ycombinator.com/item?id=17996161
Legally, if you are in the USA (or some other country surrounded by water) get on a boat, take it 5-10 miles out, and start (also when on a flight over an ocean would give you some coverage).
The comment you referred to (thank you) makes perfect sense.
I have never signed a contract with Facebook. Does that mean I’m free to reverse engineer it?
I thought this was 'hacker' news not 'let us study the click through EULA and respect the terms and conditions entirely' news.
If you can't or won't reverse engineer a binary file, you're a share cropper not a computer owner.