head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Risk of Rain demands more variance.

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

Optimization · Practiced Mastery
Side-scrolling roguelike where item synergies snowball against a relentless difficulty clock.
Grand Theft Auto V leans Execution (Practiced Mastery); Risk of Rain leans Optimization (Practiced Mastery).
Risk of Rain leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Risk of Rain
Dodging projectiles and platforming under scaling pressure.
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Risk of Rain
Enemies spawn and chase; no adaptation.
Risk of Rain leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
Risk of Rain
Item drops and stage rolls dominate run identity.
Risk of Rain leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Risk of Rain
Item stacking and time-pressure routing is solvable.
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.