I like how you express your speech in your videos it keeps the listeners attention which I think is extremely important when creating video tutorials.
Part 1: Fingers
You said:
"More mass when you need to play strong, less mass when you need to play fast"
Personally do not not see the relevance of saying this because this is not something that is happening 100% of the times when playing piano.
You also highlighted: "Fingers for speed, wrist for power speed, arms for power"
Also to me I find this a little simplistic in trying to explain these three parts of the body.
When discussing finger positions you are talking about positions where once the hand finds a position all the fingers in that position do not move at all and you spend the majority of the video explaining the c major scale then going into an example which is too difficult for beginners to comprehend.
It is a nice feeling to consider everything in piano can be worked in chunks where the hand does not have to move, however the thought process in creating these groups, how to move from one group to the other, how to move while playing particular groups, considering centers of the hand while playing the group etc etc, these issues then explode the issue of hand position into hundreds of more issues which can only be understood through detailed piece investigation.
Talking about hand position is handy, covering all notes when you move position, it is a key point when learning piano, most beginners fail it and find each note individually without one position of the hand. You should have perhaps highlighted the concept of hand position with more simple tools like a simple Hanon exercise or a much simpler piece. You should also hint on the other ways in which groups of notes have to be played, the gradual movement of different parts of our hands which allow transferring from one group to the other most effortless also how we move if playing a large position cannot be done with stagnant fingers or the art of fingering when playing Bach for instance.
If we apply the concept of controlling new positions immediately the beginner will rush the hand into the position and this will cause tension, so improvements in our efficiency as to how exactly cover new positions in the most effective manner is quite a personalized issue otherwise something that needs to be explained covering all main variants. I usually initially teach basic hand position through triad chords, scales and exercises then getting the students to practice basic pieces which use these devices.
Part 2: Wrists
Fingers do not always have to get out of the way to support the wrist action when you play octave motions. We have to have the flexibility to be able to add notes within the octaves with our other fingers and produce the same wrist action. The use of the wrist when considering your fingering is a far more instructive view on wrist action than only considering its use for fast octaves. You could have connected the wrist use with how you control what you did in your fingering video, it would make a beginners feel more secure with what you are talking about and loop your knowledge in a more logical fashion.
Part 3: Arms
Arms are used to increase accuracy and control so you need to demonstrate this more not so much the sound difference. How are arms connected to your wrist and fingering videos would be again an interesting relationship to make. For example, how are the arms used to play larger fingering positions at the piano (eg: the Chopin you play in this video perhaps you can talk about the arm in the LH arpeggio pattern a little how it helps you form the sound and control the group in one physical movement).
Topic: Piano Technique Videos - Parts of the Body