Thanks a lot for all replies! I really appreciate your help.
It is of course important to differentiate between
position and
action, as you say.
but the extreme curve of a pianist like Richter is a totally different matter
I see what you mean! I've listened a lot to Richter, but actually never noticed on video his extreme curve. Interesting to watch!

Regarding Argerich vs. Kissin: I think I was a little bit unclear. This isn't about who's best or who's playing scales clearest and producing the purest sounds etc. I'm thinking of the use of muscles etc. If you are teachers, would you teach the "Kissin technique" or "Argerich technique" (or something in between) ?
I personally think that Kissin uses the muscles in the forearm too much. I'm not criticizing him as a pianist, but I'm just discussing the "ergonomics".
Look at this video, where Argerich and Kissin play together:
You can see how "curved" (if that is the correct word) the Kissin fingers are. Look at 02:22 for example.
My thought is that he uses the flexor muscles of the forearem (to keep it curved) at the same time as he uses the extensor muscles of the forearm to lift the fingers high (see at his 5th finger particularly; it's lifted very high compared to Argerich's 5th finger).
I think that too much use of the extensor muscles and flexor muscles (which have actually quite opposing functions) at the same time is
not good (ergonomically).
I'm not saying that Argerich play the piano better, but I think that she uses the
muscles more effectively, and that her use of the intrinsic muscles of the hand (interossei and lumbricales) is better for the body.
I've played quite similiar to the Kissin technique you see in the video above at 02.22, with quite curved fingers and the 5th finger curved and lifted high. My teacher tries to show me that I should
not curve the fingers that much (by using flexor muscles in the forearm). I should have a quite small DIP and PIP angle, but a larger angle at the knuckles. The movements should be in the knuckle. This is what we observe in Argerich.
To summarize, I would say that I'm trying to have a technique where I:
- have quite small DIP and VIP angles (in "static" positions)
- the movements are made in the knuckle, i.e. I'm not curving/curling the fingers in motion as I lift them. I just try to lift them straight up without much changes in DIP or PIP angles
What do you think of my thoughts / my teacher's thoughts?
More feedback and advices is highly appreciated!