head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

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

Execution · Practiced Mastery
An open-zone Sonic experiment with cyberspace stages.
Grand Theft Auto V leans Execution (Practiced Mastery); Sonic Frontiers 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.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Sonic Frontiers
Boost-running and combat at speed
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Sonic Frontiers
Scripted enemies
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Sonic Frontiers
Static open zones
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Heists, money loops, builds learnable.
Sonic Frontiers
Skill tree and stat farming
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.