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 · Competitive PvP
Shot timing and play-calling against opponents who scheme around your habits.

Execution · Practiced Mastery
A rugby sim testing on-field execution and tactical play-calling.
NBA 2K16 leans Execution (Competitive PvP); Rugby 08 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.
NBA 2K16
Shot-stick timing and dribble moves gate every possession
Rugby 08
Timing tackles, passes and kicks needs manual skill
NBA 2K16 leans a little harder on reads, though the gap is small.
NBA 2K16
Online opponents adjust defensive schemes against your tendencies
Rugby 08
Human opponents bluff plays; AI is scripted
Rugby 08 leans a little harder on variance, though the gap is small.
NBA 2K16
Shot RNG and card packs add bounded randomness
Rugby 08
Some randomness in tackle and bounce outcomes
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
NBA 2K16
Playbooks, rotations and roster building reward deep study
Rugby 08
Play calling and team tactics are a learnable layer
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.