Depends entirely on each game. Front players tends to drag behind in eco at the beginning, but once they secure the mid resources, they have an advantage in late game. The problem is that if your team uses more players or resources than the other team to gain the middle, then they may lose if the other team's "back" players are ahead. In other words, you were inefficent, you gained less strategy value than you spent gaining middle.
These are generally noob games, and in my experience, victory is always up to the best players, doesn't really matter what the others do.
Also in those maps every player already has a lot of resources in his starting location, so you don't really need to expand.
Noobs tend to be better at ecoing up to do late game stuff than actually fighting efficently in the front, so that's why front doesn't really make a difference.
Taking mid resources should indeed give you and advantage over your opponent, but only if you do it fast enough, because the more time you spend trying to win it, the more behind you get, so you need a lot more time to make it pay off, and you are probably going to die before that happens.
This is not that big of a problem as long as the same number of players fight for the middle and waste about the same amount of resources, but if you are doing less with more, then you will get behind and your enemy will have a window of opportunity before you make those resources pay off.
Of course this only apply to noob games, because good players don't play this kind of choke point maps.
Edit.:
EvanGalea wrote:Is it because holding mid is so resource intensive that they out eco us?
Well you said it yourself