That sounds like the perfect thing to do while I'm driving.

iOS has recently added a ”trigger voice recorder” to the swipe-down screen from the lock screen.

It takes a random length of time to start recording. But it’s always too long. And it’s unreliable.

This would be much more convenient. Though I’m not sure the battery situation would convince me.

If I could press one button (and not unlock the phone) I would; my samsung even has an extra wasted button (the "bixby" button) but it isn't reconfigurable. (Still fails for the "while driving" case but I'd be using it the rest of the time)

The cellphone that’s buried in my handbag? I think you missed the expressed use case (admittedly, a few paragraphs into TFA):

”Before, I would take my phone out of my pocket to jot these down, but I couldn’t always do that (eg, while bicycling). I also wanted to start using my phone less, especially in front of my kids.”

Why stop there? Why use your phone at all? Just go visit your mum instead of calling...

Sorry the sarcasm, but not everything should need you to take your phone, unlock, get distracted, open social media on a reflex and forget what you were doing in the first place.

...and face the seductive allure of all those delicious notifications trying to get me to task switch to a bunch of other things?

No, sir. I'm pretty much on board with anything that reduces the number of times I need to light up that phone screen.