If you claim REing a flagship FAANG application is "extra easy", either they need to be laughed out of the room or you do.
Reverse engineering is easy when the source code is available. :)
The difference between source code in a high-level language, and AArch64 machine language, is surmountable. The effort is made easier if you can focus on calls to the crypto and networking libraries.
Note that WhatsApp as a web client, too: https://eprint.iacr.org/2025/794
Does FAANG apps have antidebug or code obfuscation? At least for google their apps are pretty lightly protected. The maximum extent of obfuscation is the standard compilation/optimization process that most apps go through (eg. r8 or proguard).