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

Optimization · Pure Optimization
A tower defense game with offense, sending units while defending your base.

Optimization · Pure Optimization
WWII grand strategy: templates, production, and focus paths.
Defenders of Ardania leans Optimization (Pure Optimization); Hearts of Iron IV leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Defenders of Ardania
Placing towers and units needs no physical speed
Hearts of Iron IV
pausable, micromanagement-heavy
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Defenders of Ardania
Multiplayer attack-defense adds genuine opponent prediction
Hearts of Iron IV
PvP partly, mostly scripted AI
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Defenders of Ardania
Spell outcomes and unit waves add some randomness
Hearts of Iron IV
focus tree branches, events
Hearts of Iron IV leans a little harder on optimization, though the gap is small.
Defenders of Ardania
Tower placement, unit waves and spell timing are solvable
Hearts of Iron IV
division templates and production solved
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.