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

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

Optimization · Pure Optimization
A breezy dungeon-crawling loot game about builds and ever-better randomized gear.
Fallout: New Vegas leans Optimization (Pure Optimization); Torchlight leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Torchlight
Click-to-kill combat with minimal mechanical demand
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Torchlight
Solo dungeon crawl, no adaptive opposition
Torchlight leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Torchlight
Randomized loot and dungeon layouts gate power
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
Torchlight
Build paths and gear stats are the real game
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.