head to head
Neither is simply harder - they are hard in different places. Assassin's Creed Chronicles: China demands more optimization; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
Side-scrolling stealth that rewards memorising patrols and executing clean routes.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Assassin's Creed Chronicles: China leans Optimization (Practiced Mastery); Grand Theft Auto V 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.
Assassin's Creed Chronicles: China
Stealth timing and climb precision punish sloppiness
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Assassin's Creed Chronicles: China
Guard patrols are fixed memorisable loops
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Assassin's Creed Chronicles: China
Everything is scripted and visible with study
Grand Theft Auto V
Some mission and lobby randomness.
Assassin's Creed Chronicles: China leans clearly harder on optimization.
Assassin's Creed Chronicles: China
Routing perfect-stealth paths through guard patterns is the score game
Grand Theft Auto V
Heists, money loops, builds learnable.
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.