Early med tank tank rush is doomed simply because of the nod turrets and slow rate of fire.... When turrets are destroyed, this is often mammoth time...
In AGT/Obelisk maps :
- first Nod is attacker, GDI need to defend
- then when mammoths are coming, GDI makes the siege, and Nod is defending.
Obviously this not always true, because of lack of teamplay or not, because of the skill of the players and so on...
BUT, VERY VERY OFTEN ON MAPS LIKE HOURGLASS AND CITY IF GDI DOESN'T DEFEND A BIT, THEY LOSE IN THE FIRSTS TEN MINUTES !!!
I've seen this a lot, a lot , a lot of time .... Ok you can tell me that GDI can APC rush the obelisk. True but every clever Nod player knows this too, and simply mine the obelisk. And think about, how easy is APC rush in GDI base as a Nod...
=> GDI first must defend : on defended maps that's a matter of survival.
On undefended maps that's another story...