The old test for type 2 diabetes tested the concentration of glucose in the bloodstream. Glucose persists in the bloodstream for maybe a few hours, but that time varies WIDELY. HbA1c is a protein which gets released as red blood cells glycate. HbA1c persists in the bloodstream for an average of a couple of weeks.
Blood glucose tests can yield both false positives and false negatives. Normal people can have blood glucose spikes, and type 2 diabetics can have transient low blood glucose levels. But HbA1c testing has its own problems. The test assumes that red blood cells are glycated by blood glucose. This is false. Red blood cells can get glycated by anything they touch, such as sugars which get stored in the liver.
Pharmaceutical companies added to the type 2 diabetes problem by developing drugs which lower blood glucose without lowering glycation. As HbA1c is adopted as the definitive type 2 test pharmaceutical companies are developing drugs which lower the HbA1c marker without helping type 2 diabetes.
Type 2 diabetes is caused by cellular insulin resistance. Cells become incapable of taking up glucose from the blood, and the blood fills with glucose. The definitive test for type 2 diabetes would be a measure of insulin resistance. When medical science comes up with a test for insulin resistance, then we might have something.
But even if we were to identify a marker for insulin resistance and test for that marker, pharmaceutical companies would invent drugs which treat the marker without curing insulin resistance.
What's needed? Elimination of the cause of insulin resistance. We already have a model of the cause of insulin resistance. Insulin resistance is caused by ingestion of proteins which mimic insulin. These proteins are contained in certain carbohydrate foods. And these carbohydrates are extremely addictive.