I actually take carbs at times even if Im strict meat and veggies, say a light carb sports drink with whey protein in it, and a handful of BCAAs, beta alanine, and creatine during a training session, then after a big protein shake and resume meat and veggies diet.
I think everyone is different and there is no set protocol cookie cutter for all of us to follow...surely folks have been getting lean and ripped while using wheat products, yams and potatoes, and rice for years!
I agree there are a lot of individual tolerance issues. That being said how many times a day do we see someone post they have a clean diet (eat whole grains, dairy rice etc) and simply cant cut.
Couple things to consider. Grains = gluten and for a large portion of the population gluten = problems. Next, you have the insulin factor your mentioned, lots of folks bodies over react to large carb loads. Lastly, just think how grain is stored, what comes running out of a silo when there is a grain fire? Bugs and rodents! Pissing and shitting all over the food you eat.
As power said 100g isnt a lot and if your cutting is working, likely no need to fix it BUT cutting out grains, even if you dont think there is a problem will likely speed your progress.