head to head
Helldivers 2 asks more than XCOM: Enemy Unknown, and the gap is execution.

Optimization · Practiced Mastery
Top-tier co-op shooter against bug and bot hordes.

Optimization · Systems & Chaos
Managing RNG-driven combat while solving the underlying base economy and research tree.
Helldivers 2 leans Optimization (Practiced Mastery); XCOM: Enemy Unknown leans Optimization (Systems & Chaos).
Helldivers 2 leans clearly harder on execution.
Helldivers 2
Recoil, stratagem inputs, friendly-fire aim
XCOM: Enemy Unknown
Turn-based; no twitch inputs; cover placement has mild precision
Helldivers 2 leans a little harder on reads, though the gap is small.
Helldivers 2
Enemies scripted, no adaptive opponent
XCOM: Enemy Unknown
Aliens follow scripted AI, never model your specific habits
XCOM: Enemy Unknown leans a little harder on variance, though the gap is small.
Helldivers 2
Patrol spawns and modifiers shake missions
XCOM: Enemy Unknown
Hit chances, crit rolls, and mission spawns create constant RNG swings
XCOM: Enemy Unknown leans a little harder on optimization, though the gap is small.
Helldivers 2
Loadout and stratagem synergies deep
XCOM: Enemy Unknown
Squad composition, research order, and base economy are 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.