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
Off-road simulator about hauling lumber through brutally deformable Russian mud.

Optimization · Practiced Mastery
Methodically mapping a hostile station where knowledge and routing beat reflexes.
Spintires leans Optimization (Practiced Mastery); System Shock 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.
Spintires
Throttle finesse and winching through mud need careful hands
System Shock
Combat and cyberspace ask competent but dated reflexes
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Spintires
No opponents
System Shock
SHODAN's threats are scripted, not an adapting mind
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Spintires
Terrain deforms dynamically; fuel and routes uncertain until scouted
System Shock
Citadel's layout and logs are hidden until uncovered
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Spintires
Route choice, fuel logistics, and vehicle selection decide success
System Shock
Inventory, routing and station knowledge solve the game
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.