It definitely takes some getting used to, but once you do it's such an efficient and enjoyable typing experience.
[1] https://atreus.technomancy.us/ keyboard.io also recently completed a kickstarter campaign for mass-produced Atreuses and are taking pre-orders for the next run: https://shop.keyboard.io/products/keyboardio-atreus
Maybe I just haven't fully internalized the "you'll get used to it after some time" part yet. Maybe the "some time" part is actually around six months of continuous usage instead of about three. I'm not sure.
1. It's cheaper and easier to have less switches on a board. Some people are using switches that push a dollar or more a switch. That's an extra ten bucks for keys that... most people don't use that often. It also makes it easier for board layout I imagine, but I'll admit I don't have much knowledge on creation of custom PCBs.
2. One of the things I've seen complained about with the Ergodox and the reason most of the variants (Gergo, Iris, Corne) is the same thing your friend said. The extra keys that aren't in easy reach add more hand movement. When you have a thumb cluster as a lot of these boards do adding more layers is relatively trivial. Most of these boards have software that lets you output macros as well meaning that you can essentially output key short cuts that would have used the f keys, or any other 3 plus combination of keys as just two. Germ over a Gboards has taken this concept to absurdity with the Ginny. It has ten keys and is heavily inspired by stenography style chording.
I used to be in your boat, not thinking I'd ever want something smaller then maybe a 75% or ten keyless. However I recently got a 64% keyboard that has a split space bar. I'll admit I haven't found myself missing the f keys as much as I thought I would. The closer positioning of the arrow keys has left my elbows feeling better at the end of the day. It's also close enough to a normal keyboard that even with a few substitutions (esc is now where caps lock is. Backspace is right thumb.) my muscle memory seems to be fine when switching back and forth.
Also, a lot of people seem to have macropads or separate numpads and use them for basically the exact same purpose I'm currently using the function keys for, so that could be a good compromise if I still want something like the Ergodox with a split layout.
Keeb.io has a split keyboard with F keys on top, and macro keys on the left. Not a full layout with a numpad, but getting closer. I built a Quefrency by them and like it a lot.
Is this some kind of cultural thing, where nobody in the DIY keyboard space is interested in making such a keyboard, even though there are keyboards marketed as ergonomic with cheap dome switches I don't prefer but still have function keys? Are "split keyboard" and "function keys" mutually exclusive properties? I don't understand.
EDIT: Okay, I did not look hard enough at all.
https://www.zergotech.com/
This looks like the kind of keyboard I would be interested in using.