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

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

Execution · Practiced Mastery
A stylish skate-shooter where pulling tricks reloads your guns mid-combat in a deadly blood sport.
Grand Theft Auto V leans Execution (Practiced Mastery); Rollerdrome leans Execution (Practiced Mastery).
Rollerdrome leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Rollerdrome
Trick-to-reload skating while aiming in slow motion is pure hands
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Rollerdrome
House Player enemies act on fixed behaviors
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Rollerdrome
Arenas and spawns are deterministic
Rollerdrome leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Rollerdrome
Combo routing and kill order define high scores
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.