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

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

Execution · Practiced Mastery
Neon 16-bit run-and-gun built on cover play and scripted boss duels.
Grand Theft Auto V leans Execution (Practiced Mastery); Huntdown leans Execution (Practiced Mastery).
Huntdown leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Huntdown
Cover-dodge timing and boss pattern execution
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Huntdown
Bosses telegraph on fixed scripts
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Huntdown
Minor weapon-drop variation
Huntdown leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Huntdown
Learning patterns and arena layouts
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.