Is that essentially a one way rachet? All you need to climb easily is prevention of regress and maybe some mechanical advantage, right?

It is a bit more complex. Climbing means falling. The 'ratchet' needs to work under shock loads. And wet/ice ropes radically change the friction numbers. There is a reason why climbers, experienced ones, know and use a great many different tricks for accending and decending ropes. A "big wall" climber can make a belay device out of almost anything, or even nothing.

like your hip!

“The leader must not fall.”

Aid climbing: https://en.wikipedia.org/wiki/Aid_climbing It's using techniques like that to go up rock walls instead of free climbing the rock holds.

Yes