Your dumbphone can't have your actual phone number as that SIM is in your iPhone, so it's no good for emergency notifications. The reality is that the vast majority of people can't actually use a dumbphone as their daily driver. Society has pushed us past that point.

This simply isn't true. Where I live every major operator offers multisim i.e. two (e)sims with the same number. It's primarily used for smartwatches, but they support phones as well.

Do dumb phones accept esims though? Usually they require the physical card.

A dumbphone does not have imessage, dictation, voice memos, timer, and other small things that makes life more convenient. That's why I prefer apple watch.

You could get a few of those with a HN style Rube Goldberg where you set up a VoIP you can call that will do voice to sms, call back timer, etc.