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

Optimization · Pure Optimization
The classic AD&D CRPG where party planning beats dice luck over time.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.
Baldur's Gate leans Optimization (Pure Optimization); Fallout: New Vegas leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Baldur's Gate
Pause-and-play needs minimal dexterity.
Fallout: New Vegas
Shooter inputs with VATS assist
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Baldur's Gate
Scripted encounters, no adaptation.
Fallout: New Vegas
Scripted factions and enemies
Baldur's Gate leans clearly harder on variance.
Baldur's Gate
AD&D dice rolls throughout.
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.
Baldur's Gate
Party builds and encounter prep 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.