head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Arcade driving gated by a randomised upgrade-card progression economy.

Execution · Practiced Mastery
Co-op horde shooting that tests sustained aim and defensive setup planning.
Need for Speed: Payback leans Execution (Practiced Mastery); World War Z: Aftermath 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.
Need for Speed: Payback
Arcade handling and chase setpieces need decent hands
World War Z: Aftermath
Horde shooting and melee timing carry every swarm
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Need for Speed: Payback
Cops and rivals run scripted pursuit logic
World War Z: Aftermath
Zombies are pathfinding scripts, not minds
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Need for Speed: Payback
Speed-card upgrade rolls gate progression randomly
World War Z: Aftermath
Spawn director shuffles hordes mildly between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Need for Speed: Payback
Grinding efficient builds and routes is the systems layer
World War Z: Aftermath
Class builds, defenses and weapon upgrades reward planning
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.