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

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

Optimization · Practiced Mastery
A comedic 2D stealth adventure parodying Metal Gear, built on learnable patrols and puzzles.
Grand Theft Auto V leans Execution (Practiced Mastery); UnMetal leans Optimization (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
UnMetal
Light stealth timing and boss dodging
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
UnMetal
Guards follow fixed patrol scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
UnMetal
Some unknown-first-time gags, mapped on replay
UnMetal leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
UnMetal
Routes, item puzzles, and scripted bosses are solvable
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.