Several companies provide a rtc in modular form. Most people don't need one since they enable ntp by default. And people who do just pony up the $5 or whatever, and plug one in.
Yup, yup! That's why I labeled it minor; my only complaint is it eats up valuable real-estate and can preclude using a hat. I have a cluster hat for the Pi I like to use that connects 4 pi Zeros to the pi over USB and the Pi video panel. Whether or not they use all the pins I believe they block all the pins, so it's an inconvenience.
I have the clusterHAT as well. You gotta admit it is one of the cooler rpi devices out there. It's a Big Mac sized super computer, even if it isn't truly practical; it is way cheaper than any other super computer out there, so the pi's reputation as an educational platform is accentuated.
I'm looking forward to transplanting it onto a Pi4, since it is more likely able to run the types of simulations I run, and the separation of network stacks will make it really hum. So much cheaper (and forgiving) than renting cloud instances too early on.