head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Super Metroid demands more optimization.

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

Execution · Practiced Mastery
Movement execution and route optimisation through a fixed, mappable planet.
Grand Theft Auto V leans Execution (Practiced Mastery); Super Metroid leans Execution (Practiced Mastery).
Super Metroid leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Super Metroid
Wall-jumps, shinesparks and boss dodges demand precise inputs
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Super Metroid
Bosses cycle fixed patterns, never adapting
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Super Metroid
Item and route knowledge is fixed once discovered
Super Metroid leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Super Metroid
Sequence-breaking route optimisation is the enduring meta-game
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.