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

Optimization · Pure Optimization
A VATS-heavy wasteland RPG won by perk and build optimization.

Optimization · Pure Optimization
A charming JRPG carried by familiar evolution and party-build routing.
Fallout 3 leans Optimization (Pure Optimization); Ni no Kuni: Wrath of the White Witch leans Optimization (Pure Optimization).
Fallout 3 leans a little harder on execution, though the gap is small.
Fallout 3
VATS-leaning combat, low aim demand
Ni no Kuni: Wrath of the White Witch
Hybrid action-turn combat, low input demand
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout 3
Scripted enemies
Ni no Kuni: Wrath of the White Witch
Scripted enemies
Ni no Kuni: Wrath of the White Witch leans a little harder on variance, though the gap is small.
Fallout 3
Loot rolls, SPECIAL checks
Ni no Kuni: Wrath of the White Witch
Familiar catch and drop rolls
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
Ni no Kuni: Wrath of the White Witch
Familiar evolution and party routing rewarded
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.