head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Mario + Rabbids Sparks of Hope demands more reads.

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

Optimization · Pure Optimization
A turn-based tactics game with Mario and Rabbid characters.
Fallout: New Vegas leans Optimization (Pure Optimization); Mario + Rabbids Sparks of Hope leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Mario + Rabbids Sparks of Hope
Menu-driven actions, light aim
Mario + Rabbids Sparks of Hope leans clearly harder on reads.
Fallout: New Vegas
Scripted factions and enemies
Mario + Rabbids Sparks of Hope
Some AI positioning to anticipate
Mario + Rabbids Sparks of Hope leans a little harder on variance, though the gap is small.
Fallout: New Vegas
Some loot and crit RNG
Mario + Rabbids Sparks of Hope
Hit chances and spark draws
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
Mario + Rabbids Sparks of Hope
Team comp, spark synergy, positioning
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.