head to head
Neither is simply harder - they are hard in different places. Borderlands 2 demands more execution; Crusader Kings II demands more reads.

Optimization · Systems & Chaos
Loot-shooter RPG built on gear chasing.

Optimization · Systems & Chaos
Medieval dynasty sim with chaotic event-driven stories.
Borderlands 2 leans Optimization (Systems & Chaos); Crusader Kings II leans Optimization (Systems & Chaos).
Borderlands 2 leans clearly harder on execution.
Borderlands 2
Aim matters but generous hit feel
Crusader Kings II
pausable, no reflex
Crusader Kings II leans clearly harder on reads.
Borderlands 2
Enemies are scripted loot fodder
Crusader Kings II
AI characters scripted not adaptive
Borderlands 2 leans a little harder on variance, though the gap is small.
Borderlands 2
Procedurally generated weapon drops vary
Crusader Kings II
dynastic events, traits, intrigue
Borderlands 2 leans a little harder on optimization, though the gap is small.
Borderlands 2
Skill trees and gear math heavily solved
Crusader Kings II
succession, marriages, claims plannable
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.