head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Underwater dogfighting testing piloting and aim through scripted missions.

Execution · Practiced Mastery
Third-person action where Captain Titus chainswords through ork hordes without a cover system.
AquaNox leans Execution (Practiced Mastery); Warhammer 40,000: Space Marine leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
AquaNox
Six-degree underwater dogfighting demands piloting and aim
Warhammer 40,000: Space Marine
Melee-shooting flow and execution timing carry combat
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
AquaNox
Mission enemies attack on fixed scripts
Warhammer 40,000: Space Marine
Ork hordes follow scripted aggression
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
AquaNox
Missions play out identically each attempt
Warhammer 40,000: Space Marine
Encounters are fixed and predictable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
AquaNox
Ship loadout and weapon choice add modest planning
Warhammer 40,000: Space Marine
Weapon choice and fury management are simple to learn
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.