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

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

Execution · Practiced Mastery
Crowd-control execution against memorised enemy patterns, stage by stage.
Grand Theft Auto V leans Execution (Practiced Mastery); Streets of Rage leans Execution (Practiced Mastery).
Streets of Rage leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Streets of Rage
Spacing, crowd control and throw timing carry every stage
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Streets of Rage
Enemy gangs attack from fixed arcade patterns
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Streets of Rage
Spawns are essentially deterministic per stage
Streets of Rage leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Streets of Rage
One-credit clears come from learned positioning and patterns
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.