head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Vandal Hearts II demands more reads.

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

Optimization · Pure Optimization
A tactical RPG testing positioning and turn prediction on a grid battlefield.
Fallout: New Vegas leans Optimization (Pure Optimization); Vandal Hearts II leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Vandal Hearts II
Simultaneous-turn combat has no twitch input
Vandal Hearts II leans clearly harder on reads.
Fallout: New Vegas
Scripted factions and enemies
Vandal Hearts II
Predicting AI move order matters but follows scripts
Vandal Hearts II leans a little harder on variance, though the gap is small.
Fallout: New Vegas
Some loot and crit RNG
Vandal Hearts II
Hit chances add bounded randomness
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
Vandal Hearts II
Unit positioning, builds and the prediction system win battles
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.