head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

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

Optimization · Pure Optimization
An open world where build optimisation dissolves every combat challenge.
Fallout: New Vegas leans Optimization (Pure Optimization); The Elder Scrolls V: Skyrim - Special Edition leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Shooter inputs with VATS assist
The Elder Scrolls V: Skyrim - Special Edition
Combat timing matters little; difficulty bends to your build
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
The Elder Scrolls V: Skyrim - Special Edition
Draugr and dragons run scripted AI packages
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Some loot and crit RNG
The Elder Scrolls V: Skyrim - Special Edition
Loot rolls and radiant quests add minor mapped randomness
Fallout: New Vegas leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
The Elder Scrolls V: Skyrim - Special Edition
Perk, crafting and stealth-archer loops trivially solve combat
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.