head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Kirby's Dream Course demands more optimization.

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

Optimization · Practiced Mastery
A golf-puzzle hybrid where Kirby is the ball and every hole has a plannable optimal line.
Grand Theft Auto V leans Execution (Practiced Mastery); Kirby's Dream Course leans Optimization (Practiced Mastery).
Kirby's Dream Course leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Kirby's Dream Course
Power and spin must be set with fine precision
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Kirby's Dream Course
No adaptive opponent in solo play
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Kirby's Dream Course
Fully deterministic boards
Kirby's Dream Course leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Kirby's Dream Course
Each hole is a solvable angle-and-power puzzle
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.