The 3500 mile interval was established (by oil change companies) long before synthetic oils became common. It just doesn't apply to today's oils. Thanks you for the information posted !
In 2004 I bought a Ford pickup for work with a V8. I changed the oil every 10-15000 miles. Let it idle for hours at times. Sold it at 150,000 to a friend who is towing a classic car with it. We hauled horses with it weekly. Synthetic oil.
