head to head
Neither is simply harder - they are hard in different places. Arcanum: Of Steamworks and Magick Obscura demands more variance; Fallout: New Vegas demands more execution.

Optimization · Pure Optimization
A Victorian-era RPG where the magic-versus-tech split and schematic mastery reward deep system optimization.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Arcanum: Of Steamworks and Magick Obscura leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Arcanum: Of Steamworks and Magick Obscura
Real-time mode is optional; turn-based eliminates all twitch
Fallout: New Vegas
Shooter inputs with VATS assist
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Arcanum: Of Steamworks and Magick Obscura
All NPCs and factions follow scripted dialogue and combat routines
Fallout: New Vegas
Scripted factions and enemies
Arcanum: Of Steamworks and Magick Obscura leans clearly harder on variance.
Arcanum: Of Steamworks and Magick Obscura
Hidden technology diagrams and faction reaction thresholds create exploration unknowns
Fallout: New Vegas
Some loot and crit RNG
Arcanum: Of Steamworks and Magick Obscura leans a little harder on optimization, though the gap is small.
Arcanum: Of Steamworks and Magick Obscura
Magic versus technology stat split and schematic discovery 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.