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

Optimization · Pure Optimization
Dystopian management adventure about a landlord spying on tenants for a totalitarian state.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Beholder leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Beholder
Simple point-and-click landlord actions
Fallout: New Vegas
Shooter inputs with VATS assist
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Beholder
Tenants follow scripted schedules, not adaptive
Fallout: New Vegas
Scripted factions and enemies
Beholder leans clearly harder on variance.
Beholder
Tenant events and directives surprise first runs
Fallout: New Vegas
Some loot and crit RNG
Fallout: New Vegas leans a little harder on optimization, though the gap is small.
Beholder
Money, time, and blackmail decision routing
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.