Yea I see the fact of less contamination, but oil still breaks down. Heat/cool cycles, condensation and bearing material still have a factor in the longevity of oil.
When you seal off the rotating assembly from the valvetrain, you do not have the hydrocarbons contaminating the oil.
No expert on oil, but would say that the major issue is contamination. Look at rear gear oil...100k miles, sealed, no contamination, only heat and pressure.
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1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
