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

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

Execution · Practiced Mastery
Aiming precision and shot planning across sixty deterministic pool tables.
Grand Theft Auto V leans Execution (Practiced Mastery); Lunar Pool leans Execution (Practiced Mastery).
Lunar Pool leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Lunar Pool
Cue angle and power precision decide every pocketed ball
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Lunar Pool
Alternating-turn pool offers nothing to predict in an opponent
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Lunar Pool
Tables are fixed; physics are deterministic per friction setting
Lunar Pool leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Lunar Pool
Planning shot order and leave across 60 tables rewards 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.