head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Pure Mechanics
Routine shooter aim through scripted cartel firefights.

Execution · Pure Mechanics
Era-typical scripted WWII shooting galleries testing aim and placement memory.
Call of Juarez: The Cartel leans Execution (Pure Mechanics); Medal of Honor: Rising Sun leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Juarez: The Cartel
Standard FPS gunfights run on aim alone
Medal of Honor: Rising Sun
Aim against scripted soldier placements is the core demand
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Juarez: The Cartel
Co-op secret objectives add mild teammate suspicion
Medal of Honor: Rising Sun
Multiplayer adds light human prediction; campaign AI is static
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Juarez: The Cartel
Enemy waves spawn identically each run
Medal of Honor: Rising Sun
Setpiece missions replay identically
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Juarez: The Cartel
Weapon levelling is a thin progression layer
Medal of Honor: Rising Sun
Memorising enemy placements and routes is shallow but present
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.