head to head
Neither is simply harder - they are hard in different places. Angry Birds 2 demands more variance; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
Slingshot trajectory puzzles with randomised bird hands gating consistency.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Angry Birds 2 leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Angry Birds 2
Trajectory precision on the slingshot matters modestly
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Angry Birds 2
Pigs sit in structures, never adapting
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Angry Birds 2 leans clearly harder on variance.
Angry Birds 2
Random bird-card hands and multi-stage levels shuffle each attempt
Grand Theft Auto V
Some mission and lobby randomness.
Angry Birds 2 leans a little harder on optimization, though the gap is small.
Angry Birds 2
Knowing structure weak points and bird matchups is the edge
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.