Each unit connected to the network that is not attacking supports one other attacking unit. Having all units connected to the network attacking of course leaves no capacity for supporting other units. Also, as one unit can only support one other unit at a time, you need 6 times the number of attacking entities connected to the network to make full use of it. If there are more than 6 supporters, more units get buffed until all support capacity is used.
If each connected entity would buff every other entity, it would be vastly overpowered as the attack power would scale exponentially with power cost, overshadowing all other playstyles. You would practically be creating combat power out of thin air.
Root is still very strong, especially defending choke points with little space to place multiple towers. Root nexus makes the defence self sufficient in most cases, so you don't even have to pay attention to it.