Your comments in that thread bring up some interesting points. I'm not sure I agree with all of them but they are well argued and a good read.
Principle of the Offensive: Hinjo launching attacks against a superior force before repelling the initial assault would be foolish. Defenders can launch counter assaults and raids, but they need to be planned carefully so your troops aren't cut off (esp. when outnumbered 3/1). For example, opening your gates to send out skirmishers when they are under direct attack is risky at best.
Principle of the Objective: Without a clear understanding of how much Hinjo thought his forces could hurt Xykon beforehand, it makes sense when you remember what he said: They are there as reinforcements for the Sapphire Ghost army. In fact, Hinjo's statements in 449 make it clear that he knows he is sending them there to die so they can come back as (presumably) more powerful ghost warriors. In fact, looking at the nature of the strip, it almost appears that you have to have the failure (and death) for the ghost-martyrs to kick in. Given that, he has to put SG members there.
Hinjo specifically indicates that he believes Roy and group are the only ones able to handle Xykon (in living state anyway) which is why he sends them to deal with Xykon as they see fit. Since for Hinjo protecting the gate is the utmost priority, he has to put his SG members in the throne room so they can fight, die, and be activated as ghost martyrs when/if Xykon gets that far. I think he's working from the assumption that if Roy and gang can't stop Xykon, then Xykon will make the throne room, so the strongest possible defense of the gate itself has to be the main focus for the SG.
Of course, this is bad for the rest of the city and the other troops. But it does help showcase conflicting loyalties. Ultimately, Hinjo's first duty seems to be to his oaths as a member of the SG, not to his people. He is concerned about them, but he's making plans based on defending the gate specifically.