head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Optimization · Systems & Chaos
Optimizing Grey Knight loadouts and campaign decisions against escalating Bloom infection timers.

Optimization · Systems & Chaos
Seminal 1994 strategy game mixing global base management with brutal turn-based alien squad combat.
Warhammer 40,000: Chaos Gate - Daemonhunters leans Optimization (Systems & Chaos); X-COM: UFO Defense leans Optimization (Systems & Chaos).
Warhammer 40,000: Chaos Gate - Daemonhunters leans a little harder on execution, though the gap is small.
Warhammer 40,000: Chaos Gate - Daemonhunters
Turn-based; Willpower and cover angle require spatial not twitch skill
X-COM: UFO Defense
Turn-based; only inventory clicking
Warhammer 40,000: Chaos Gate - Daemonhunters leans a little harder on reads, though the gap is small.
Warhammer 40,000: Chaos Gate - Daemonhunters
Chaos AI follows scripted threat escalation patterns
X-COM: UFO Defense
Alien AI is scripted, never adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Warhammer 40,000: Chaos Gate - Daemonhunters
Nemesis Force activations, random Bloom spread, and loot drops create variance
X-COM: UFO Defense
Hit rolls, random maps, and unseen aliens punish constantly
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Warhammer 40,000: Chaos Gate - Daemonhunters
Grey Knight wargear, psychic powers, and campaign priority are tightly optimizable
X-COM: UFO Defense
Base economy, research order, and tactical doctrine are masterable
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.