head to head
Neither is simply harder - they are hard in different places. Giga Wing demands more execution; Grand Theft Auto V demands more reads.

Execution · Practiced Mastery
Arcade shmup famous for its bullet-reflect barrier and scores running into the quintillions.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Giga Wing leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Giga Wing leans clearly harder on execution.
Giga Wing
Reflect-timing and dodging under heavy fire
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Giga Wing
Scripted waves with no adaptation
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Giga Wing
Deterministic patterns around the reflect mechanic
Grand Theft Auto V
Some mission and lobby randomness.
Giga Wing leans clearly harder on optimization.
Giga Wing
Reflect-force timing and medal routes set astronomical scores
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.