head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

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

Execution · Practiced Mastery
An open-world romp where the President of the United States gets superpowers inside an alien simulation.
BioShock 2 leans Execution (Practiced Mastery); Saints Row IV 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.
Saints Row IV
Superpowered movement and shooting are fast but forgiving
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
BioShock 2
Splicer AI scripted, not adaptive.
Saints Row IV
Simulation enemies run fixed scripts
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.
Saints Row IV
Mild spawn and sandbox randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
BioShock 2
Plasmid combos and gear loadouts solvable.
Saints Row IV
Power upgrade paths trivialise the simulation once optimised
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.