Some great putters may be better be stronger at one aspect than another, but overall they must have a certain level of competency at all four...
Aim
Our ability to aim the putter correctly to our desired start line is an ability not often talked about when it comes to putting, or indeed the rest of the game when is comes to the clubface.
Green reading is irrelevant if we simply cannot aim to our desired start line, and with compensations often being made to achieve the desired result, consistency is difficult.