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

Optimization · Pure Optimization
An open-world RPG mostly about discovering and stacking exploitable progression systems.

Optimization · Pure Optimization
Faithful X-COM successor managing a global war against alien invasion.
The Elder Scrolls V: Skyrim leans Optimization (Pure Optimization); Xenonauts leans Optimization (Pure Optimization).
The Elder Scrolls V: Skyrim leans clearly harder on execution.
The Elder Scrolls V: Skyrim
Combat is forgiving; aim and timing rarely punish you.
Xenonauts
Turn-based; no physical demands.
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
Enemy AI is scripted and exploitable; not adaptive.
Xenonauts
Alien AI follows consistent behavior rules.
Xenonauts leans clearly harder on variance.
The Elder Scrolls V: Skyrim
Loot tables and leveled lists inject mild randomness.
Xenonauts
Hit rolls and unseen alien positions punish certainty.
Xenonauts leans clearly harder on optimization.
The Elder Scrolls V: Skyrim
Skill stacking, enchant loops, and exploits are deeply solvable.
Xenonauts
Air war, economy and squad doctrine decide campaigns.
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.