This is probably true, though fwiw I use penzoil platinum. Mobil 1 apparently just isn't quite as good these days and penzoil plat shows up well with analyses. My cars do have synthetic from factory and the brand name stuff from the dealership is too expensive.Doesn't make a damned bit of difference...
OE is Wix07 Cadillac CTS 3.6L - Mobil 1 Synthetic 5W30 / AC-Delco Filters
Amsoil oil and filter. 1 year or 25k miles, whatever comes first.
That is a lot!
I change every 7k miles.