head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Hello Kitty's Cube Frenzy demands more optimization.

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

Optimization · Practiced Mastery
A block-stacking puzzle about building paths to collect items.
Grand Theft Auto V leans Execution (Practiced Mastery); Hello Kitty's Cube Frenzy 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.
Hello Kitty's Cube Frenzy
Block placement timing needs light dexterity
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Hello Kitty's Cube Frenzy
Solo with no opponent to predict
Hello Kitty's Cube Frenzy leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Hello Kitty's Cube Frenzy
Falling block colors add some randomness
Hello Kitty's Cube Frenzy leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Hello Kitty's Cube Frenzy
Planning staircases and color matches solves levels
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.