Oil filter change vs oil change

I used to work for a small now extinct oil company, as a truck driver. I was some what close to the ops mgr. He told me that oil didn't break down, it was contamination. I would also go along with modifiers.
AMSOIL as I think back, started this change the oil filter and add oil thing. Seems like back in the '80's. They were one of the first commercial synthetic companies. Found out not to use synthetic grease in boat trailer wheel bearings, synthetic grease won't mix with water, regular grease does.