head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
An open world where build optimisation dissolves every combat challenge.

Optimization · Pure Optimization
Planning stealth routes around fully mappable guard patterns.
The Elder Scrolls V: Skyrim - Special Edition leans Optimization (Pure Optimization); Thief 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.
The Elder Scrolls V: Skyrim - Special Edition
Combat timing matters little; difficulty bends to your build
Thief
Movement timing matters but shadows forgive imprecision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
The Elder Scrolls V: Skyrim - Special Edition
Draugr and dragons run scripted AI packages
Thief
Guards patrol fixed routes with mappable vision cones
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
The Elder Scrolls V: Skyrim - Special Edition
Loot rolls and radiant quests add minor mapped randomness
Thief
Patrol layouts are scripted-but-unknown on first entry
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
The Elder Scrolls V: Skyrim - Special Edition
Perk, crafting and stealth-archer loops trivially solve combat
Thief
Route planning around guard patterns is the whole game
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.