I made my first sourdough with tangzhong a couple of years ago using Foodgeek's technique. The roux is 20% of the recipe and he says you can go as high as 40%. Maybe that's why you didn't see results.
I always bake an extra loaf for my neighbor and I didn't tell him that I did anything different. He asked me the next day what I changed. He noticed a much softer crumb. As far as shelf life; who cares? My sourdough always gets devoured within a day or 2.
But yes, if done properly, you will DEFINITELY see a diffence in the crumb; even with your cinnamon rolls.

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