Being forceful helps because with more strength and size behind him, Warnock would have been more effective making it harder for the player in question to mark the ball!
And if you were watching Essendon (which is a stupid question, im sorry), there was only ever two of those players in the forward 50 as one had to be in the ruck, whereas Collingwood had Wood.
The amount of ball making them more effective is true, but this is about who would have been more effective in curbing one of them and I say Warnock.