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

Optimization · Practiced Mastery
Solving fixed environmental puzzles by trial and error, with light timed stealth.

Optimization · Practiced Mastery
Routing efficient digs and upgrades through a randomised mine.
Black the Fall 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.
Black the Fall
Some timed stealth and chase sections demand light precision
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.
Black the Fall
Guards and machines run fixed detection scripts
SteamWorld Dig
Enemies follow simple fixed patterns
SteamWorld Dig leans a little harder on variance, though the gap is small.
Black the Fall
Puzzle mechanics are unknown until each trial-and-error death
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.
Black the Fall
Each room is a fixed puzzle with one solution
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.