head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Medal of Honor: Frontline demands more optimization.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
A cinematic WWII console shooter famous for its D-Day opening.
Grand Theft Auto V leans Execution (Practiced Mastery); Medal of Honor: Frontline leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Medal of Honor: Frontline
Console gunplay through cinematic set-pieces
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Medal of Honor: Frontline
Scripted soldiers never adapt
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
Medal of Honor: Frontline
Set-piece surprises fade after one run
Medal of Honor: Frontline leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Medal of Honor: Frontline
Memorising spawns and routes trivialises missions
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.