Note that modern flip/soapbar phones (Commodore, KaiOI) usually support some social media, including WhatsApp.
Banking apps are a problem though, and really contribute locking everyone in the iOS/Android duopoly, and that sucks.
The way I imagined it is that I'd still have my main smartphone at home and maybe for office days at work, but bring the other one when I go out, to visit friends or family, etc. Being out and about is where I think not having the attention-grabbing and distractions is most important. At home, I feel like I personally can control it quite well myself.
It's the very idea of having two devices instead of one that still keeps me from these things, though. Even if I only ever had one with me, that's still about twice the work of maintenance, updates, remembering to charge, having two lines...