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.
