Do you have any idea hot hot the valves are when the engine is running. Oil running down the stem turns to varnish before it reaches the seat. You wouldn't see the oil that makes it into the engine burn as it is a very small amount compared to blow by with bad rings. Just think how frequently you topped off your oil. Probably didn't even register on the dip stick, but you can see evidence of oil in the varnish and tar that remains.
Anything running down the exhaust valve would burn in the exhaust pipes without affecting performance. But if oil gets into the combustion chamber it lowers the octane rating of the fuel resulting in knocking, which forces you to retard the spark and loose possible performance.
All of this is speculation without a further examination.