head to head
Neither is simply harder - they are hard in different places. Just Act Natural demands more variance; Nidhogg demands more execution.

Reads · Pure Mind Games
Behavioural bluffing - mimicking NPCs while human seekers learn your tells.

Reads · Competitive PvP
Minimalist fencing duel that is almost entirely about out-guessing one human.
Just Act Natural leans Reads (Pure Mind Games); Nidhogg leans Reads (Competitive PvP).
Nidhogg leans clearly harder on execution.
Just Act Natural
Walking like an NPC needs restraint, not dexterity
Nidhogg
Sword-height changes and dive-kicks need quick hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Just Act Natural
Out-guessing human seekers and hiders is the whole game
Nidhogg
Pure human duels of feints and conditioning
Just Act Natural leans clearly harder on variance.
Just Act Natural
NPC crowds and tasks add cover noise
Nidhogg
Symmetric deterministic arenas
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Just Act Natural
Task patterns can be learned but humans counter-adapt
Nidhogg
Small toolkit, little to solve beyond fundamentals
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.