head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Mega Man 11 demands more execution.

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

Execution · Practiced Mastery
Modern Mega Man adding a slow-motion gear system to classic stage design.
Grand Theft Auto V leans Execution (Practiced Mastery); Mega Man 11 leans Execution (Practiced Mastery).
Mega Man 11 leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Mega Man 11
gear-swap platforming demands quick precise inputs
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Mega Man 11
bosses cycle fixed movesets
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Mega Man 11
fully deterministic stages
Mega Man 11 leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Mega Man 11
weakness order plus Double Gear timing strategy
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.