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

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

Optimization · Pure Optimization
Colonize Mars by stacking dome layouts and supply chains.
Fallout: New Vegas leans Optimization (Pure Optimization); Surviving Mars leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Surviving Mars
pausable, no reflex
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Surviving Mars
no adversary
Surviving Mars leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Surviving Mars
disasters, sponsor traits
Surviving Mars leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Surviving Mars
dome layouts and supply chains
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.