head to head
Neither is simply harder - they are hard in different places. Anno 1800 demands more optimization; The Elder Scrolls V: Skyrim demands more execution.

Optimization · Pure Optimization
Beautiful 19th-century city-builder ruled by production ratios.

Optimization · Pure Optimization
An open-world RPG mostly about discovering and stacking exploitable progression systems.
Anno 1800 leans Optimization (Pure Optimization); The Elder Scrolls V: Skyrim leans Optimization (Pure Optimization).
The Elder Scrolls V: Skyrim leans clearly harder on execution.
Anno 1800
pausable, no twitch
The Elder Scrolls V: Skyrim
Combat is forgiving; aim and timing rarely punish you.
Anno 1800 leans a little harder on reads, though the gap is small.
Anno 1800
AI scripted, not adaptive
The Elder Scrolls V: Skyrim
Enemy AI is scripted and exploitable; not adaptive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Anno 1800
minor trade fluctuations
The Elder Scrolls V: Skyrim
Loot tables and leveled lists inject mild randomness.
Anno 1800 leans clearly harder on optimization.
Anno 1800
supply chains and ratios are the game
The Elder Scrolls V: Skyrim
Skill stacking, enchant loops, and exploits are deeply solvable.
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.