Out balls. Having a big man gives you something to launch balls at in the hope he'll hold it up whilst you push out. When we don't have that we have to try to play out from the back or we lose possession and that makes us predictable and easy to play against.
Ideally we'd have a big man and someone with pace so we have the option to go long if we need to. It makes it harder to stop us.
But conversely, when teams come to defend against us having two little ones can be an advantage as the movement is usually better and can drag defenders around.
I'm afraid I'm a bit like NA in that I think all the team defends and all the team attacks so you have to look at how a player affects both aspects. For example, having a slow defence means you tend to sit deeper which affects how you attack.
Sorry, I wasn't being flippant, I'd just assumed you'd got what I meant but disagreed.