Obviously the Fighting-
Though there are sub-games for air or sea travel and combat these seem to be rare edge cases that would be filled by very specialized Ranger or Fighter offshoots that few would play unless the campaign centered on it. The Cleric is binary here- depending on edition and build the Cleric is a master or all or none with a default to magical healing. Which highlights the problems of the class in my opinion. But also stands him up as a counterpoint to the Magic-User and the Fighter.
It seems that this would lead t the idea that what classes you have in your game are dependent on if you want an adventuring archetype to dominate a particular sub-game, or do you want that shared? Classes that share archetypes would be interesting. Again a Ranger with a more limited combat ability compared to the Fighter seems like it would be the poster boy for this approach. Also there is the idea of building out the base archetypes to share in the sub-games the other classes dominate.
It seems the Thief was an interesting design accident that could be used as an example for the future game development. What seems to have happened in a subconscious collective sort of way was that players understood that there was a sub-game of dungeon exploration that The Cleric, Fighter, and Magic-User while dominating their own parts of the game were not masters of. Ergo the Thief develops. It seems it would come back to essential spotlight time. Is it shared or not?