Gonna argue with both of you... oil filters screen down to their pore diameter and then they're done. If they contain a magnet, as some do, that helps with smaller ferrous particles, but not stainless or aluminum. Will your repurposed bar oil come out of a Franz oil filtration tech demo unit or out of a regular car with a Walmart filter?
Cummins equals big diesel, and a million miles is high mileage but not crazy high for those engines. Plus those engines have much larger clearances for oil flow than gas engines, a much greater oil system capacity, and they flat out don't wear down as fast because there's more oil in bigger channels lubricating the moving parts. Show me a Honda Civic with the original engine and 500,000 miles on it... 500k is kind of the minimum expectation for big diesel.
Back to gas engine land, when you rebuild a high mileage engine, one of the regular things you probably need is cylinder polishing and maybe even boring and bigger rings. All that missing metal went somewhere, and the cylinders aren't the only thing in the oil path that wears down. That's not an unexpected problem- it's just wear.
So I agree there's probably minimal metal in Granny's oil when she drove 1000 miles a year and then got an oil change, but I don't agree that a bucket of black goo from the auto shop has the same thing going on.