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

Optimization · Pure Optimization
A tower-defense gacha where carefully placed operators hold lanes against scripted waves.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Arknights leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Arknights
Deployment is unhurried and pausable
Fallout: New Vegas
Shooter inputs with VATS assist
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Arknights
Enemies follow published routes
Fallout: New Vegas
Scripted factions and enemies
Arknights leans clearly harder on variance.
Arknights
Gacha rolls shape your roster
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.
Arknights
Operator placement puzzles are fully solvable
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.