head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

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

Optimization · Pure Optimization
A puzzle-combat Paper Mario built around rotating rings.
Fallout 3 leans Optimization (Pure Optimization); Paper Mario: The Origami King 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
Paper Mario: The Origami King
Light timing on action commands
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
Paper Mario: The Origami King
Scripted enemies
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
Paper Mario: The Origami King
Limited puzzle 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
Paper Mario: The Origami King
Ring puzzle solving and accessory loadouts
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.