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

Optimization · Systems & Chaos
Isolating targets amid randomised crowds using traps and patience.

Optimization · Practiced Mastery
Routing efficient digs and upgrades through a randomised mine.
Party Hard leans Optimization (Systems & Chaos); SteamWorld Dig leans Optimization (Practiced Mastery).
SteamWorld Dig leans a little harder on execution, though the gap is small.
Party Hard
Walking and stabbing need timing but little dexterity
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.
Party Hard
Partygoers wander on RNG, not adaptive minds
SteamWorld Dig
Enemies follow simple fixed patterns
Party Hard leans a little harder on variance, though the gap is small.
Party Hard
Random traps, events and witness behaviour vary each level
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.
Party Hard
Trap usage and isolation tactics converge to known strategies
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.