I completely disagree with you about this. If there were a riot in Washington D.C., you wouldn't tell the Secret Service officers to leave the presidents side to go help to local cops.
If the secret service was full of overpowered super soldiers that could dish out more pain than all of the cops in DC combined and the president was in a location that required special means to gain entrance into I would.
It doesn't make sense that the 0 squad didn't help which is what Soifon was pointing out. If they are more powerful than the 13 squads, which includes Yamamoto the guy that incinerated several of the invaders on his own, had they sent 2-3 people down to SS this crap would be over. Yes, their job is to protect the king, but damn it weren't they watching the fight ?
Several captains survived their battles even with their Bankai being locked due to the circumstances, meaning the enemy wasn't that freaking powerful. From where I'm standing the opportunity for a surprise attack in order to end things was there. As for the king, it has been established that you need a key or some other shit to make it to his realm/palace so he/she/it would not be in immediate danger.
Not only was their inaction a stupid move but it all seems to stem from arrogance.
"You do your job I do mine. Even though had I helped you things would be over by now and there would have been a lot less casualties."
That is just shitty writing in my opinion.
What if the Quincy had developed their own way of entering the Kings Palace that nobody new about and only invaded SS as a mean of distracting the Zero Squad so another Quincy Team could kill the King while he's undefended. I'm not saying that's the plan, but people in their positions have to think about all the possibilities, and take cautions against these things.
Also what would happen if the Quincy had stole the powers from Zero Squad? SS (and the rest of the universe) would be completely beyond fucked. Perhaps some counter measure against them will now be developed that will give the Zero Squad (and the rest of SS) an edge in the next battle that they would have lacked had they come in and fought (and horribly died) in the last fight.
While these are reasonable, possible scenarios I don't think the events of the manga back it up. Let's be real here, the only worth while person among the Quincy was Juha. Ganking the bastard and ending shit would have been the right move. As for the Quincy possibly having the means to get into the palace, wouldn't it have been a much more effective strategy to go to the palace directly ?
The element of surprise would cause disarray among the royal guard making them too occupied to fetch help from the 13 squads, and should the Quincy be victorious it would leave the King exposed. Engaging the lower troops in this case would be retarded as it would alert the royal guard and give them a chance to observe the Quincy in action.
Edit: Just to add to my comment about Juha being the only threat.
He was the only one that could steal Yama's Bankai, meaning had he not been there the old man would have cleaned the house. If the 5 can produce even the low figure of twice the Old man's power there was no way Juha would have been able to withstand a group attack since he had to render Yama Bankailess before taking him out.