Not necessarily. You only have to overcome the dilution on specific dimensions. Suppose everyone mates only on intelligence, and marries a person of exactly equal genetic intelligence to themselves. Then there's no dilution per generation on intelligence, though there is on e.g. height.

The question here is why names are so highly predictive.

It seems highly unlikely that each generation would be selecting on precisely the same genetic features of a particularly prominent family name. This is because that which provides social prominence is not consistent over time.