head to head
Neither is simply harder - they are hard in different places. Deadly Premonition demands more variance; Fallout: New Vegas demands more execution.

Optimization · Pure Optimization
A famously janky open-world horror mystery where FBI agent Francis York Morgan investigates a small-town murder.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Deadly Premonition leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Deadly Premonition
Clunky combat is forgiving and rarely the obstacle
Fallout: New Vegas
Shooter inputs with VATS assist
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Deadly Premonition
Shadows and the Raincoat Killer follow fixed scripts
Fallout: New Vegas
Scripted factions and enemies
Deadly Premonition leans clearly harder on variance.
Deadly Premonition
Town schedules and side content are unknown until discovered
Fallout: New Vegas
Some loot and crit RNG
Fallout: New Vegas leans a little harder on optimization, though the gap is small.
Deadly Premonition
Time management, schedules, and routing dominate completion
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.