head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Incubation: Time Is Running Out demands more variance.

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

Optimization · Pure Optimization
A turn-based squad tactics game about positioning marines against hidden aliens.
Fallout: New Vegas leans Optimization (Pure Optimization); Incubation: Time Is Running Out leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Incubation: Time Is Running Out
Turn-based, no aiming or timing skill needed
Incubation: Time Is Running Out leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Incubation: Time Is Running Out
Alien AI is scripted, ambush-driven not adaptive
Incubation: Time Is Running Out leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Incubation: Time Is Running Out
Hidden enemies around corners create real uncertainty
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
Incubation: Time Is Running Out
Squad positioning and tactical planning win the missions
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.