head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Fire Emblem Echoes: Shadows of Valentia demands more variance.

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

Optimization · Pure Optimization
Remake of Gaiden with dual protagonists and explorable dungeons.
Fallout: New Vegas leans Optimization (Pure Optimization); Fire Emblem Echoes: Shadows of Valentia leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Fire Emblem Echoes: Shadows of Valentia
Turn-based menus only
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Fire Emblem Echoes: Shadows of Valentia
Scripted enemies on both routes
Fire Emblem Echoes: Shadows of Valentia leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Fire Emblem Echoes: Shadows of Valentia
Hit RNG plus dungeon encounters
Fallout: New Vegas leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Fire Emblem Echoes: Shadows of Valentia
Dual-army routing and class promotions
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.