head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Practiced Mastery
Big Daddy POV return to Rapture with tighter combat systems.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
BioShock 2 leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
BioShock 2
Dual-wield drill and gun timing matter.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans a little harder on reads, though the gap is small.
BioShock 2
Splicer AI scripted, not adaptive.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
BioShock 2
Sister-gathering waves add randomness.
Grand Theft Auto V
Some mission and lobby randomness.
BioShock 2 leans a little harder on optimization, though the gap is small.
BioShock 2
Plasmid combos and gear loadouts solvable.
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.