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
A minimal physics puzzle about chaining explosions to reach the goal.
Fallout 3 leans Optimization (Pure Optimization); Zup! X 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
Zup! X
Minimal dexterity to trigger explosions
Fallout 3 leans a little harder on reads, though the gap is small.
Fallout 3
Scripted enemies
Zup! X
Solo - no opponent to model
Fallout 3 leans a little harder on variance, though the gap is small.
Fallout 3
Loot rolls, SPECIAL checks
Zup! X
Deterministic physics puzzles, no hidden 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
Zup! X
Finding the right explosion sequence is the puzzle
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.