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

Optimization · Pure Optimization
Gunpowder-era Total War blending empire management with line battles.

Optimization · Pure Optimization
WWII grand strategy: templates, production, and focus paths.
Empire: Total War 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.
Empire: Total War
Real-time battle micro is modest
Hearts of Iron IV
pausable, micromanagement-heavy
Hearts of Iron IV leans a little harder on reads, though the gap is small.
Empire: Total War
Multiplayer line-battle feints exist
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.
Empire: Total War
Campaign AI and battle dice noise
Hearts of Iron IV
focus tree branches, events
Hearts of Iron IV leans a little harder on optimization, though the gap is small.
Empire: Total War
Campaign economy and line-infantry tactics are mappable
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.