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

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

Optimization · Pure Optimization
Open-area SMT where essence customization and Press Turn mastery turn demons into solvable math.
Fallout: New Vegas leans Optimization (Pure Optimization); Shin Megami Tensei V leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Shin Megami Tensei V
Open-field exploration, but combat is pure menus.
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Shin Megami Tensei V
Magatsuhi and bosses are scripted patterns.
Shin Megami Tensei V leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Shin Megami Tensei V
Crit and negotiation RNG add manageable noise.
Shin Megami Tensei V leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Shin Megami Tensei V
Essence fusion and Press Turn builds reward perfect planning.
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.