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

Optimization · Pure Optimization
The deepest optimization puzzle in the Infinity Engine lineage, rewarding encyclopedic knowledge of 2nd Edition AD&D systems.

Optimization · Pure Optimization
A post-nuclear RPG expanded in scope where tagged builds and Gifted-trait optimization dominate.
Baldur's Gate II: Shadows of Amn 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.
Baldur's Gate II: Shadows of Amn
Pause-and-plan removes twitch entirely; micro-placement has marginal value
Fallout 2
Turn-based AP system makes twitch entirely irrelevant
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Baldur's Gate II: Shadows of Amn
Enemies run scripted behaviour patterns, never modelling your tactics
Fallout 2
All tribal and Enclave enemies run fixed scripted combat routines
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Baldur's Gate II: Shadows of Amn
Loot randomization and enemy ability use create hidden-information layers
Fallout 2
Hidden special encounters and timed events create significant unknown-information space
Baldur's Gate II: Shadows of Amn leans a little harder on optimization, though the gap is small.
Baldur's Gate II: Shadows of Amn
Mage spell sequences, dual-class builds and Spellhold routing define mastery
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.