Smart Switch doesn't transfer login credentials, because usually you need to register and login a change of device anyway, like with bank and financial apps, which is for security.
I used Smart Switch when I went from a Huawei Mate10 to a Galaxy Note20 Ultra, and that certainly transferred all my WhatsApp data. However it still did all the security stuff with using a new device, same for my WeChat, AliPay, TaoBao, Trip, apps, etc.