Wow! A1c from 12.3 down to 6.3................... what a drastic improvement! Great for you.

You took your health by the horns and drastically improved it. At 12.3 that blood sugar level was doing great damage to your organs and tissues. That improvement will help keep a lot of other common health diseases at bay. Most of the common non-infection diseases can be directly linked to insulin resistance as either the cause or major contributing factor. By controlling it you greatly improve your chance of success of either not getting those diseases or greatly reducing their significance or time frame during your lifespan.

The latest bad thing, covid, was directly linked to obesity being a contributing factor for poor outcomes. There is a pretty good chance that insulin resistance was the underlying real cause and the obesity was just the symptom that manifested itself and was the visible portion so got noticed.

Could it also have to do with vitamin D resistance???? Vitamin D has also been found to be important in covid. Here is a researcher that talks about vitamin D resistance and insulin resistance being possibly associated.  https://www.youtube.com/watch?v=RfH8nkF-R5c&t=1550s