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

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

Optimization · Pure Optimization
Maxis simulation where you guide a black ant colony to conquer a suburban yard.
Fallout: New Vegas leans Optimization (Pure Optimization); SimAnt leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
SimAnt
Light direct ant control; spider dodging is mild dexterity.
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
SimAnt
Red colony AI is scripted behaviour, never models you.
SimAnt leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
SimAnt
Spider, rain, lawnmower and yard events are random hazards.
Fallout: New Vegas leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
SimAnt
Caste ratios, pheromone trails and expansion order are solvable.
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.