When it comes to balance, each player has easy access to about the same number of stars (about 13). There will be a bit of an advantage for blue and green here, as their stars are more concentrated and will give their fleets easier access to the front lines. Far from being an advantage, though, that may just serve as some balance to being stuck in the center and being accessible from all three enemies.
I would also guess that any game with this setup will end with a cold war. Players only have one direction to go, which takes them away from the frontlines. No one is going to want to commit to moving forward until they’ve gotten enough of an advantage to take and hold some territory, but with everyone following the same strategy, I can see where stagnation could occur.
As a possible fix, what if starting positions were moved back off the frontline by about 3 stars? This would give players/teams the option to sprint forward to gain the middle territory, but give up the demilitarized zone, or move away from the front to consolidate a safe base of operations, or both, depending on teamwork. I think that might inject a bit more variability into the game and would allow the teams to work more closely together on creating a strategy.