head to head
Neither is simply harder - they are hard in different places. Empire: Total War demands more reads; Fallout: New Vegas demands more execution.

Optimization · Pure Optimization
Gunpowder-era Total War blending empire management with line battles.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Empire: Total War leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Empire: Total War
Real-time battle micro is modest
Fallout: New Vegas
Shooter inputs with VATS assist
Empire: Total War leans clearly harder on reads.
Empire: Total War
Multiplayer line-battle feints exist
Fallout: New Vegas
Scripted factions and enemies
Empire: Total War leans a little harder on variance, though the gap is small.
Empire: Total War
Campaign AI and battle dice noise
Fallout: New Vegas
Some loot and crit RNG
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Empire: Total War
Campaign economy and line-infantry tactics are mappable
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.