head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, 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 · Pure Optimization
Diablo-styled survivors-like with classic CRT dungeon aesthetics.
Diablo III leans Optimization (Pure Optimization); Halls of Torment leans Optimization (Pure Optimization).
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
Halls of Torment
Auto-attacking with positional dodging, low skill ceiling.
Diablo III leans a little harder on reads, though the gap is small.
Diablo III
No meaningful adaptive opponent; co-op is cooperative
Halls of Torment
Scripted enemy waves.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Diablo III
Primal Ancient drops and set dungeon RNG drive the grind
Halls of Torment
Drops and trait rolls shape builds.
Diablo III leans a little harder on optimization, though the gap is small.
Diablo III
Set bonuses and paragon levelling are almost entirely solvable
Halls of Torment
Stat stacking and trait synergies reward solving.
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.