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

Execution · Competitive PvP
Shot-timing execution and play-calling prediction against human or scripted defenses.

Execution · Competitive PvP
Shot timing and play-calling against opponents who scheme around your habits.
NBA 2K12 leans Execution (Competitive PvP); NBA 2K16 leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K12
Shot timing and stick handles decide possessions
NBA 2K16
Shot-stick timing and dribble moves gate every possession
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K12
Online opponents bait defenses and adapt play calls
NBA 2K16
Online opponents adjust defensive schemes against your tendencies
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K12
Shot RNG adds bounded noise to outcomes
NBA 2K16
Shot RNG and card packs add bounded randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K12
Play calling, rosters and matchup exploits are studied systems
NBA 2K16
Playbooks, rotations and roster building reward deep study
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.