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 VATS-heavy wasteland RPG won by perk and build optimization.

Optimization · Pure Optimization
An open-world RPG mostly about discovering and stacking exploitable progression systems.
Fallout 3 leans Optimization (Pure Optimization); The Elder Scrolls V: Skyrim 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.
Fallout 3
VATS-leaning combat, low aim demand
The Elder Scrolls V: Skyrim
Combat is forgiving; aim and timing rarely punish you.
Fallout 3 leans a little harder on reads, though the gap is small.
Fallout 3
Scripted enemies
The Elder Scrolls V: Skyrim
Enemy AI is scripted and exploitable; not adaptive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout 3
Loot rolls, SPECIAL checks
The Elder Scrolls V: Skyrim
Loot tables and leveled lists inject mild randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout 3
Perk and build planning carries the run
The Elder Scrolls V: Skyrim
Skill stacking, enchant loops, and exploits are deeply solvable.
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.