The reason I say insulin resistance leads to bad control is because if I eat tons of carbs for a week and don't exercise, my insulin requirements go up. I need more basal and more bolus, because as I'm putting more insulin into my body my cells become more resistant. If after that week I switch my diet to a totally healthy diet, where all my foods have low GI, my insulin requirements are still high. I am more resistant to insulin now, than I was before I ate tons of carbs for a week.
In the second week, even though I'm eating healthy and avoiding high GI food, I'm still having to take large amounts of insulin to deal with small amounts of low GI foods. Now if on that first week I had eaten healthy, avoided high GI foods and exercised 5 times for an hour, I am much more sensitive to insulin when the second week starts. My insulin requirements have lowered and insulin reacts much faster in my body. This means after meals I don't spike at all and I'm constantly below 8mmol/l, whereas when I am insulin resistant even healthy meals make me spike to 12mmol/l+. This means my average sugar level is much, much better, along with all the health benefits of having less insulin in my system.