For me, it takes between 10 hours (worst case) to 5 minutes (best case) to open WhatsApp.
My iPhone 4S is too old, so opening WhatsApp gives a message "This version of WhatsApp ha..., Update WhatsApp, Your update will be free of cha...". Clicking Update WhatsApp opens the App Store, and clicking Update results in another error message: "This application requires iOS 10.0 or later."
So I only use WhatsApp through BlueStacks Android emulator on my personal laptop. That's what leads to the 10 hour worst-case response time: a full working day, including commute. The 5 minute best-case is because BlueStacks takes a very long time to open, and runs my laptop fans really loud.
This is not only a pain point with WhatsApp, it's also a problem with WeChat, KakaoTalk, LINE, even 9gag (for posting videos).
Meanwhile, email continues to work just fine on my decade-old phone, mbasic.facebook.com is particularly speedy, iMessage still works, and Hacker News is great :)
https://faq.whatsapp.com/web/download-and-installation/how-t...
If they tried to make a shared framework that ran the same codebase everywhere and then port it onto different platforms (cough facebook) then you don't get these nice isolated issues, for example.
All these requirements are like saying "having a good experience using this app requires an app that doesn't crash all the time". Well, duh?