head to head
Neither is simply harder - they are hard in different places. Devil May Cry 5 demands more execution; Grand Theft Auto V demands more reads.

Execution · Practiced Mastery
Modern stylish-action peak with three playstyles and a combo ceiling players are still climbing.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Devil May Cry 5 leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Devil May Cry 5 leans clearly harder on execution.
Devil May Cry 5
Three movesets and Royal Guard frames set a towering ceiling
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Devil May Cry 5
Even Vergil's mirror fight is a learnable script
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.
Devil May Cry 5
V's summons add flavor, not randomness that matters
Grand Theft Auto V
Some mission and lobby randomness.
Devil May Cry 5 leans clearly harder on optimization.
Devil May Cry 5
Loadouts, breakers, and enemy-specific tech reward deep study
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.