......“has been accepted”......
ok, I’ll concede that statement as too specific.
My personal physician made the diagnosis after watching the fasting glucose results for a while. He than introduced the A1c and it now seems to be the primary number in spite of considerable variance in the fasting glucose.
I think perhaps your fixation on cost is misplaced because to obtain a continuous data stream, it is necessary to record fasting sugar daily and plot a curve. Then take the curve and plot a moving average. Why bother? The A1C does the job nicely while eliminating a lot of bother and other tests.
This is especially true for those of us at the low end of the numbers.
I was able to rely more on the HbA1C before I started insulin. I need the instant feedback to control dosage, in part.
My fixation on cost isn’t the consumer end, but rather the producer end. I’m afraid I have become fairly jaded regarding the incidence of monetary considerations infecting legal and medical decisions. Honestly, I would be surprised if there wasn’t lobbying for this outcome by the HbA1C labs or test kit makers. After all, some of the biggest proponents of the child-safety-seat laws (now up to 8 years old in some places!) were the child-seat makers.
In my industry (safety critical software), the small, in-process verification steps are complementary to the larger, milestone steps. I see the daily (or more often) plasma glucose reading as the self-check, with the HbA1C as the higher-level check.