A better test would be to remove the chain from the bike and spin the rear wheel and see how much time it takes to coast down. Your spin test however includes rachet drag which might differ dramatically between different hubs. The seal will spin along with the outer race and hence the seal is subject to centrifugal force.
In a bicycle hub the inner race is stationary while the outer race is spinning. At higher speeds the seal is actually not making full contact with the inner race. The reason why drag seal doesn't correlate to rotational speed linearly is because at higher rotation speeds the contact seal 'lifts' up from the inner race due to centrifugal force. So if you have a bare bearing and spin it in your hand, the seal drag that you feel is not indicative of the drag in the real-world at normal speeds. Bm0p700f is saying that as the wheel speed increases bearing drag seal becomes less and hence it becomes irrelevant at normal riding speeds.
