head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Super Mario 64 DS demands more execution.

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

Execution · Practiced Mastery
A 3D platformer where precise movement and camera mastery unlock its many challenges.
Grand Theft Auto V leans Execution (Practiced Mastery); Super Mario 64 DS leans Execution (Practiced Mastery).
Super Mario 64 DS leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Super Mario 64 DS
precise 3D platforming and camera control
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Super Mario 64 DS
scripted enemies, no adaptation
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 Mario 64 DS
minimal randomness
Super Mario 64 DS leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Super Mario 64 DS
star routes and speedrun tech solvable
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.