head to head
Cossacks 3 asks more than Hearts of Iron IV, and the gap is reads.

Optimization · Pure Optimization
A large-scale real-time strategy game about massive army economies in the 17th century.

Optimization · Pure Optimization
WWII grand strategy: templates, production, and focus paths.
Cossacks 3 leans Optimization (Pure Optimization); Hearts of Iron IV leans Optimization (Pure Optimization).
Cossacks 3 leans a little harder on execution, though the gap is small.
Cossacks 3
unit micromanagement under real-time pressure
Hearts of Iron IV
pausable, micromanagement-heavy
Cossacks 3 leans clearly harder on reads.
Cossacks 3
human opponents bluff builds and attacks
Hearts of Iron IV
PvP partly, mostly scripted AI
Hearts of Iron IV leans a little harder on variance, though the gap is small.
Cossacks 3
minor combat outcome randomness
Hearts of Iron IV
focus tree branches, events
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Cossacks 3
massive army economy and tech optimization
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.