I think he was also quite good in Bronco Billy.
Wayne himself said something to the effect of “I don’t act, I react.”
John Wayne’s directors all wanted him to act like John Wayne. Just like Eastwood’s early directors wanted him to act like Eastwood. The only way Eastwood broke out of that was by becoming his own director.
That is true of many top actors.
True of most actors. That’s how the lines are written, how they’re directed. The audience has expectations for genre movies, no need to let acting get in the way.