"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.