AK is the better hand and you will come out ahead in the long run if you keep taking this bet.
AK is a 65.2% favorite AK vs. 89 (when all cards are same suit)ex AsKs 8s9s
AK is a 62.1% favorite AKs vs. 89s (when one hand is suited and the other hand is suited in a differnet suit) ex AsKs 8h9h

It doesn't matter if one has a higher probability of making a straight or any other hand. It only matters which hand has the highest probability to make the best hand.