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

Optimization · Practiced Mastery
Community resource management under randomised zombie pressure, with light action execution.

Optimization · Practiced Mastery
Routing efficient digs and upgrades through a randomised mine.
State of Decay leans Optimization (Practiced Mastery); SteamWorld Dig leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
State of Decay
Melee and driving are functional, not demanding
SteamWorld Dig
Digging and platforming need modest precision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
State of Decay
Zombies swarm by simple rules, never adapting
SteamWorld Dig
Enemies follow simple fixed patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
State of Decay
Dynamic events, infestations and survivor traits roll randomly
SteamWorld Dig
Randomised mine layouts hide ore and hazards each run
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
State of Decay
Base building, resource runs and survivor management are the game
SteamWorld Dig
Upgrade routing and efficient dig paths drive progress
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.