head to head
Neither is simply harder - they are hard in different places. Dune: Spice Wars demands more reads; Fallout: New Vegas demands more execution.

Optimization · Pure Optimization
A 4X-strategy hybrid about controlling Arrakis through economy and intrigue.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Dune: Spice Wars leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Dune: Spice Wars
Low-APM real-time control
Fallout: New Vegas
Shooter inputs with VATS assist
Dune: Spice Wars leans clearly harder on reads.
Dune: Spice Wars
Human multiplayer politics adapt; AI doesn't
Fallout: New Vegas
Scripted factions and enemies
Dune: Spice Wars leans clearly harder on variance.
Dune: Spice Wars
Map layout, sandworms, and hidden intel
Fallout: New Vegas
Some loot and crit RNG
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Dune: Spice Wars
Spice economy, councils, and tech are deeply optimizable
Fallout: New Vegas
Faction routing, perks, builds heavily 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.