Maybe I'm misunderstanding something here.
Dual Control:
Actions taken by different operators to affect a change.
Split Knowledge:
Information needed to affect a change is split between different operators.
If I have split knowledge, I must have at least 2 operators.
It follows that I must have actions take by different operators to use the information ergo dual control.
So if this is right: Can split knowledge always be considered more secure than dual control?