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

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

Optimization · Pure Optimization
A minimalist side-scrolling strategy where a mounted monarch drops coins to build walls against nightly greed raids.
Fallout: New Vegas leans Optimization (Pure Optimization); Kingdom: New Lands leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Kingdom: New Lands
Just riding and coin-dropping under time pressure
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Kingdom: New Lands
Greed waves follow deterministic escalation
Kingdom: New Lands leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Kingdom: New Lands
Island layouts and vendor spawns randomise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Kingdom: New Lands
Expansion order and economy timing decide survival
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.