head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Practiced Mastery
Tests kart-racing line execution across three vehicle types with item luck on top.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Diddy Kong Racing DS leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Diddy Kong Racing DS leans a little harder on execution, though the gap is small.
Diddy Kong Racing DS
Drift boosting across car, hover and plane handling
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Diddy Kong Racing DS
AI rivals are scripted; multiplayer prediction stays shallow
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Diddy Kong Racing DS leans a little harder on variance, though the gap is small.
Diddy Kong Racing DS
Balloon item pickups swing race positions
Grand Theft Auto V
Some mission and lobby randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Diddy Kong Racing DS
Zipper routes and vehicle choice per track are learnable
Grand Theft Auto V
Heists, money loops, builds learnable.
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.