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.

Execution · Pure Mechanics
Arcade reflex shooting under timers with memorisable rescue routes.

Execution · Pure Mechanics
Push-forward arena FPS where movement and aim are the whole game.
Alien Syndrome leans Execution (Pure Mechanics); DOOM (2016) leans Execution (Pure Mechanics).
DOOM (2016) leans a little harder on execution, though the gap is small.
Alien Syndrome
Dodging swarms under a bomb timer is pure arcade reflex
DOOM (2016)
Aim, movement, glory-kill timing all peak.
DOOM (2016) leans a little harder on reads, though the gap is small.
Alien Syndrome
Aliens swarm on fixed spawn logic
DOOM (2016)
Demons scripted attack patterns.
Alien Syndrome leans a little harder on variance, though the gap is small.
Alien Syndrome
Hostage and weapon spots are unknown until learned
DOOM (2016)
Minimal encounter randomness.
DOOM (2016) leans a little harder on optimization, though the gap is small.
Alien Syndrome
Routes to hostages and boss patterns are fully mappable
DOOM (2016)
Rune and weapon mod picks meaningful.
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.