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 · Pure Optimization
A pure loot-and-build treadmill where set-bonus optimisation and Rift pushing define performance.

Optimization · Systems & Chaos
A bleak survival narrative about a plague engulfing a steppe town.
Diablo III leans Optimization (Pure Optimization); Pathologic 2 leans Optimization (Systems & Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Diablo III
Greater Rift pushing has minor mechanical demand in builds
Pathologic 2
Combat is clumsy but matters.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Diablo III
No meaningful adaptive opponent; co-op is cooperative
Pathologic 2
NPCs are scripted, not adaptive.
Pathologic 2 leans a little harder on variance, though the gap is small.
Diablo III
Primal Ancient drops and set dungeon RNG drive the grind
Pathologic 2
Hunger, infection, and supplies fluctuate.
Diablo III leans a little harder on optimization, though the gap is small.
Diablo III
Set bonuses and paragon levelling are almost entirely solvable
Pathologic 2
Brutal resource and time scheduling is core.
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.