Gathering all your resources in one place is not practical, especially against an enemy such as the Shivans. Firstly, a substantial part of your defensive force will get massacred by swarms of fighters and bombers pouring through the node. Secondly, Shivan juggernauts exploding will do significant damage to your warships. Furthermore, your ships will need resupplying. The Sathanes would not all come through at once, if they wait a few days, sending through a few scouts to check for activity every now and again, you'll end up with massive logistics problems. The swarms of Shivan fighters coming through will go for your supply convoys instead of your warships, and your destroyers will have to withdraw to resupply, exposing weaknesses in your line of defence.
Even if you could avoid these problems, if the Shivans find another node into GTVA space, a Sathanas with accompanying fleet (Ravana, Demon, Cruisers) could raze all your planets in a few systems before you have a chance to do anything about it.
EDIT: By the way, there are 2 nodes from Capella to GTVA space, spreading your defensive line thinner.