I have several kites of two different makes. One has below the bar depower which I hate, and it seems you have the same issue trying to depower while the front lines are loaded. I could never do it with one hand. I modified the bar and put a pulley on the top of the depower line making it a 2/1 ratio, and I used smaller spec line on the rope. And though I still hate below the bar depower, at least I can depower it with one hand anytime. Anything less than that is no good in my book. If you can't shut the kite down to its limit quickly then you need another system. This kite does flag to a single line and when things go pear shaped, or if I am trying to self land in 40 knots then I just hit the release and it falls out of the sky harmlessly. Not sure how many twists there would have to be in the line before that failed, but it has not happened yet.
My other kites give you the choice to flag to single or both front lines, I choose single for my style of riding, (mainly in waves on a surfboard). It has above the bar depower and is easy to operate. Saying that though this kite is the best gust handling kite I have ever flown. When others are complaining how gusty and bad the conditions are I never really feel the same as they do. However, if I ride my other kites, I notice it straight away. I could have safely handled a 10 meter kite with those gusts. Would I enjoy it? Probably not. However, it would get me safely to the beach to either wait it out, or pump up a smaller kite.
In saying all of that, I still can't believe an instructor would not have come to your aid ASAP. We all know how quickly things turn from bad to worse.
Glad you did not get hurt, nor anyone else.