Which option is better while applying a formula: 1 list (4 items) & 1 Line-item or 4 Line items?
In terms of time-saving/performance.
Logically, you will not create 4 line items for 4 items of the list. It goes against Scalability principle of Anaplan.
You should create a single line item dimensioned by the list (of 4 items) and write a formula in the PLANUAL way.
Hope that helps