"Proper" makes sense until it doesn't. When you play the piano there are all kinds of recommended fingerings, until you realise that you don't have the same shaped hand as the person who recommended them or you started on a different finger so can't quite get into the optimal fingering.
Worse (IIRC), "proper" touch typing exists in a vacuum and has no context of the prior keypresses - rotating fingers or even switching hands at the boundary is going to lead to faster typing when you remove the artificial restrictions of "proper" typing.
BUT when you cannot touch type at all the notion of "proper" fingering provides a framework to work within and helps to form best practices that combat things like "press every key with index finger".
You'll see this in many skills and sports:
Beginner - no knowledge of the rules
Intermediate - can apply the rules
Expert - breaks the rules to achieve greater performance
Master - creates new rules
Ultimately the best fingering for touch typing is the one which leads you to type the fastest and most accurate with the least amount of energy/effort. Achieving the optimal fingering as declared by someone else isn't really the goal.
One of the rules I break on standard ANSI US keyboards is typing c and m with my index finger instead of my middle finger. Other keys in the bottom row are shifted out by one finger, and my pinkies are relieved of bottom row duty, besides the shift key. This makes a regular keyboard more like a linear (matrix) keyboard, with angled columns.
I do this because I keep my hands angled a little bit inward, to avoid the awkward and un-ergonomic bend in my wrist. That is, if standard position is like this:
I am a vim user and didn't remap esc. I use my ring or middle finger to hit esc which means I leave the home row (shock horror) but my wrist moves less far than if I use my pinky and I can find the home row again without looking
Hand angles and wrist position are somewhat glossed over if you only know "finger x presses key y"
If you think about violin and guitar - you learn how to play the same note from different hand positions so there is some (small) potential for this on the keyboard
True, but linear keyboard force you to use proper touch typing because the keys are too far for anything else. I wouldn't recommend them, even though I otherwise love mine.
Worse (IIRC), "proper" touch typing exists in a vacuum and has no context of the prior keypresses - rotating fingers or even switching hands at the boundary is going to lead to faster typing when you remove the artificial restrictions of "proper" typing.
BUT when you cannot touch type at all the notion of "proper" fingering provides a framework to work within and helps to form best practices that combat things like "press every key with index finger".
You'll see this in many skills and sports:
Beginner - no knowledge of the rules Intermediate - can apply the rules Expert - breaks the rules to achieve greater performance Master - creates new rules
Ultimately the best fingering for touch typing is the one which leads you to type the fastest and most accurate with the least amount of energy/effort. Achieving the optimal fingering as declared by someone else isn't really the goal.