I just checked with the native WhatsApp client on Windows 11: 650 MB of RAM as it is running, across all its processes. Thus, taking ≈⅓ of RAM is nothing to brag about for a reimplementation that focuses on being lean and fast. Also, "opens in under a second" – back in the days when SSDs where new, programs opened instantaneously (<60 ms)!

Lastly, I still have to be convinced that Rust is a good choice for GUI programs, considering their messy mutable state and ownership.