head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Knights of the Old Republic II: The Sith Lords demands more variance.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.

Optimization · Pure Optimization
A broken-system RPG where influence manipulation and prestige class chaining produce dominant power spikes.
Fallout: New Vegas leans Optimization (Pure Optimization); Knights of the Old Republic II: The Sith Lords leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Knights of the Old Republic II: The Sith Lords
Pseudo-turn-based d20 system makes twitch irrelevant throughout
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Scripted factions and enemies
Knights of the Old Republic II: The Sith Lords
Influence system uses scripted dialogue triggers, no adaptive opponent
Knights of the Old Republic II: The Sith Lords leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Knights of the Old Republic II: The Sith Lords
Influence thresholds and hidden stat distributions create first-play unknowns
Knights of the Old Republic II: The Sith Lords leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Knights of the Old Republic II: The Sith Lords
Prestige class chaining and influence-stat transfer create near-broken optimization ceilings
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.