head to head
Neither is simply harder - they are hard in different places. Plague Inc: Evolved demands more variance; The Elder Scrolls V: Skyrim demands more execution.

Optimization · Pure Optimization
Engineer a pandemic; evolution order is the puzzle.

Optimization · Pure Optimization
An open-world RPG mostly about discovering and stacking exploitable progression systems.
Plague Inc: Evolved leans Optimization (Pure Optimization); The Elder Scrolls V: Skyrim leans Optimization (Pure Optimization).
The Elder Scrolls V: Skyrim leans clearly harder on execution.
Plague Inc: Evolved
no reflex
The Elder Scrolls V: Skyrim
Combat is forgiving; aim and timing rarely punish you.
Plague Inc: Evolved leans a little harder on reads, though the gap is small.
Plague Inc: Evolved
world response scripted
The Elder Scrolls V: Skyrim
Enemy AI is scripted and exploitable; not adaptive.
Plague Inc: Evolved leans clearly harder on variance.
Plague Inc: Evolved
country event timing
The Elder Scrolls V: Skyrim
Loot tables and leveled lists inject mild randomness.
Plague Inc: Evolved leans clearly harder on optimization.
Plague Inc: Evolved
evolution order heavily solved
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.