It's slow and tedious to dial numbers with many high digits in them. And there's no quick dial function for commonly used numbers. Both of these things directly impact UX.

You can always dial zero and get an "operator".

An operator is like Siri or Alexa, but capable of passing a Turing test.

And now I want to build a rotary phone that connects to Alexa when you dial zero.

Don't be that evil, at least connect it to something more useful, like Google assistant.

Assuming we’re comparing stuff you can buy at a random shop:

- you can blindly hit the keys on a dial pad if you remember their position, on a rotary you probably need to count the clicks

- on a rotary you probably can’t look back at the number you already inputed

- traditional ones won’t have * and #

- no speakerphone feature, which many older people would benefit of

- no mute

- no phone number memory/speed dial

It’s actually fun to think about how much it has changed since the earlier phones, as the land lines are progressively getting obsoleted as well.

I could imagine a modern version of the rotary UI, as a swipe input interface for instance, but it would still be clunky IMO

"Intuitiveness" is AKA "resembling the current norm" when it comes to UX. Updating an aging UI to fit current patterns makes it more cohesive with the operating system, attracts more new users, and avoids confusing those new users.

Attempting to paint "strong usability" through the lens of existing users only (the guy who already knows how to use a rotary phone) is a lopsided view of the goals for an app creator.