I actually agree with the vet in this case. Having personal experience and knowledge doesn't replace a medical degree and license. Human diabetics do go the doctor a minimum of every 3 months for basic monitoring and dosage adjustment by their doctors. They are supposed to adjust their insulin according to their doctor's prescription. There is some leeway to that, of course, and they are specifically educated about this. But most human diabetics are on short acting insulin or 2 different kinds of insulin. They have basal insulin, sliding scale insulin (correction), and insulin for food. This is all carefully given. The way your protocol works, you're meshing it all together which is different. You're using a long-acting insulin and treating it like sliding scale, by dosing based on blood sugar value. Most vets dose a standard amount which would be more like a basal or food dose (maybe both). The variation in insulin dosing is more likely to lead a fluctuations in BG. You're just chasing sugars over a longer period and not really accounting for food eaten. Regardless of carb content, all calories affect blood glucose, just at a different rate.
To Shanti's mom: Its up to you how you decide to manage your cat but from your vet's perspective, it can be very difficult to help you if you aren't willing to work with her. Maybe you can find a way to compromise on a protocol? It sounds like the scale she gave you was an attempt to do that on her part. I know you care very much about your kitty and want to do what's best for it. Sometimes you just have to try one thing at a time. There isn't a wrong way to take care of him, it's always a journey figuring out what works best sometimes it changes over time. You're doing just fine.