Galactic War broken?

Everything that crzydroid said, but I would add that healing is a paramount consideration, as is some combination of healing immunity and/or strong single attacks. 

If you want to use 1 team against many nodes (which you do) that team can't be slowly whittled down. Phoenix is great for this, but doesn't have the healing immunity or offence that you sometimes need. Jedi Bastila is fantastic bc she provides a huge pool of bonus protection at the start of each fight, so enemies can knock off all of that and you'll be back up to full on the next node. Jedi Knight Anakin can provide healing immunity to a Jedi team so you can beat those annoying passive-healers like Kanan & Kylo Ren Unmasked. You can also use Padawan Kenobi and Master Qui Gon under Bastila -- together they pack a huge punch. At low levels, one of the most powerful teams is Bastila (Lead) + JKA, MQG, POW + 1 healer. You won't need your healer often, but when you do, you really do to just keep a character alive at the end of the fight so they will be there to regain all their bonus protection at the beginning of the next fight. 

Other good GW squads include NightSisters, who have a lot of healing + Daka for revives, which allows them to fight multiple nodes in a row. 

I generally don't use tanks except KRU, Kanan - with their passive healing they can keep themselves alive - and NightSister Zombie, who auto-revives and has a lot of team healing around her. Other tanks concentrate fire on themselves when, at this level, you really want the enemy to be spreading the damage around. That said, Old Ben can occasionally be useful for his AoE Ability Block. You might want to use him once on an early node to give him some turn meter than put him on the bench until / unless you hit a node where you really need that Ability Block. (Unfortunately after that you might have to use him on the next node as well -  being careful not to taunt - to get his Ability Block off cooldown in case you need it again later). 

I have a main account that is 13M gp, but I also have a baby account, just level 58, so I've been doing all this recently and am familiar with best GW strategies for low-level accounts (including which toons are available at relatively low levels). Feel free to ask more questions if you have them.