I don't know how far I've gone on the road to understanding - not very far, I'm certain - but I know I have had similar thoughts. However, some of my thoughts seem to differ from yours in detail, and if you don't mind me sharing them here, they may offer you an extra signpost or two.I remember looking at that game several times, and each time not understanding the significance of those three stones. For me, they seemed like kikashi: Black answered below, so there is no loss in throwing them away. Definitely not key stones. I always thought that maybe there is a lesson here that I failed to understand.
Where we definitely seem to differ is that you wrote "key stones". I wrote "keystone". I infer therefore that you are understanding the term as "important stones". That's not quite right. Keystone is an architectural term for a specific stone that holds an arch together. All stones in the arch are obviously important, but the keystone rather more so. In addition, the pre-westernised Japanese version of the term (kaname ishi) has some quite different connotations. There is a shrine somewhere in Japan (I've forgotten the name) with a famous kaname ishi which has nothing at all to do with arches, but is a huge stone whose purpose is to "soothe" earthquakes, and so stop the wooden shrine connected to it from falling down. Viewing Go's three stones, and similar groupings, as that kind of stone formation makes a lot more sense to me in go than visualising Norman arches and western churches. I then make a further leap of imagination and see GSG's three-stones as Athena's spear as fending off Kitani's attempts to shake the earth - Athena, goddess of wisdom and battle strategy, having the nerve to take on mighty Poseidon. (That's partly stimulated by the big difference in body frames of Go and Kitani. Just the way my mind works.)
Calling them pivot stones has similar problems. Kaname is said to derive from kani no me (crab's eye), me (eye) being a common word for a hole. The (Japanese) keystone is put in that hole. The hole, not the stone, represents the pivot. And hole can be simply a depression at some mid-point in the opponent's position. It doesn't have to be a cut. Again, I personally find it very helpful to visualise the go term in this "etymological" way.
As to the function of kaname ishi, a word association I like to use is "disruptive". I see a lot of AI play as disruptive, whereas as humans have an urge to be creative (literally so, rather than imaginative). And that should come as no surprise. Go is game of alternating turns. At literally very single step of the game, the opponent is disrupting what you have just tried to create. Learning to handle that disruption is very hard - as Kitani found. I have no idea how to do it, but I sense it may be a matter of mindset rather than technique. In the same way that people usually think only of magnets attracting (magnetic personality, and so on) and forget they also repel, I think go players think too much of creating territories, bases, moyos, and too little of disrupting. They don't forget it entirely, simply because the alternating flow of the game forces them to acknowledge it. But masters like GSG and AI really take it on board, and I think that disruption (not destruction, such as with invasions) is what we are seeing when linchpin stones (kaname ishi) work successfully.
Maybe we should call them banjax stones. Ian might agree
on D-16, which Elf recommends, would bear a relation to 
which Go Seigen likes in his Go Seigen: 21st Century Go series. Note that this position could be reached by a transposition of 
becomes urgent in the top right corner. After the ponnuki in the bottom right, the right side becomes more urgent that the top side, which explains why 
, 
has a reducing (i.e.,disruptive) effect on any Black development of the right side.
- 
, hasn't made much difference. The influence of the two stones towards the top side and center has increased that of the one stone, while the influence towards the right side has diminished little, if at all. OC, Black's center has been strengthened. 
at a seems to be a serious mistake.
makes a base on the left side. 
and 
then counteract the influence of the two stones on the top side, something that would not have been so urgent with only one White stone in the top right.
extends on the right side and after the approach of 
. If 
Black makes territory on the top side, countering White's influence there.
.
freely extends to R-10. 
pretty well nullifies it. The game develops normally through 
. 
was a counter-hane at a, and Go Seigen actually ended up saving the three stones. Elf prefers b, c, d, or e instead, by about 5% each.