head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Lara Croft and the Guardian of Light demands more optimization.

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

Optimization · Practiced Mastery
Isometric co-op action puzzler that mixes twin-stick combat with tomb puzzles.
Grand Theft Auto V leans Execution (Practiced Mastery); Lara Croft and the Guardian of Light leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Lara Croft and the Guardian of Light
Twin-stick aiming and timed platforming under fire
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Lara Croft and the Guardian of Light
Enemies spawn in fixed scripted waves
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Lara Croft and the Guardian of Light
Levels deterministic once seen
Lara Croft and the Guardian of Light leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Lara Croft and the Guardian of Light
Puzzle solutions, relic loadouts, and score routing
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.