I have the great privilege of being able to live a boring life. My country is politically stable, and I neither have personal enemies nor do I need to protect sensitive information.
Accordingly, my threat model is quite simple: I mainly want to avoid tracking (Big Tech), have control over my data, and not be too distracted from real life. And if I can protect myself from greater dangers in the process, I see that as a very welcome side effect.
I can now understand well that there are people who really should avoid dumbphones. If I understand you correctly, this mainly applies to activists, journalists, politicians, opposition members, politically persecuted people, or people who possess valuable information.
I’m quite sure that I wouldn’t be worth all that effort.
My main concern was simply not to unknowingly expose myself to an unforeseen risk.