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

Optimization · Pure Optimization
Dystopian border-checkpoint sim where stamping passports fast enough feeds your family.

Optimization · Practiced Mastery
Routing efficient digs and upgrades through a randomised mine.
Papers, Please leans Optimization (Pure Optimization); 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.
Papers, Please
Document-checking speed directly pays the rent
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.
Papers, Please
Entrants are generated, not adaptive opponents
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.
Papers, Please
Random entrant documents and scripted-event surprises
SteamWorld Dig
Randomised mine layouts hide ore and hazards each run
Papers, Please leans a little harder on optimization, though the gap is small.
Papers, Please
Internalizing rulebooks and inspection workflow efficiency
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.