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
The genre-defining loot ARPG whose builds, runes, and trade economy players still optimize decades later.

Optimization · Pure Optimization
A post-nuclear RPG expanded in scope where tagged builds and Gifted-trait optimization dominate.
Diablo II leans Optimization (Pure Optimization); Fallout 2 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 II
Positioning and potion reflexes, little else physical
Fallout 2
Turn-based AP system makes twitch entirely irrelevant
Fallout 2 leans a little harder on reads, though the gap is small.
Diablo II
Monster AI is fully mappable
Fallout 2
All tribal and Enclave enemies run fixed scripted combat routines
Diablo II leans a little harder on variance, though the gap is small.
Diablo II
Loot RNG and random maps drive the grind
Fallout 2
Hidden special encounters and timed events create significant unknown-information space
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Diablo II
Builds, breakpoints, rune economy, magic-find routing are the game
Fallout 2
SPECIAL and skill tagging with Gifted trait produce well-known dominant build strategies
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.