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

Optimization · Pure Optimization
Space 4X with politics and faction-specific economies.

Optimization · Pure Optimization
A turn-based strategy game where building the optimal army and economy decides victory.
Endless Space 2 leans Optimization (Pure Optimization); Heroes of Might and Magic 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.
Endless Space 2
turn-based
Heroes of Might and Magic IV
no real-time physical skill needed
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Endless Space 2
AI scripted, some MP
Heroes of Might and Magic IV
predicting human opponent strategy in PvP
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Endless Space 2
system traits, anomalies
Heroes of Might and Magic IV
combat rolls and map resources random
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Endless Space 2
economy, ships, populations solvable
Heroes of Might and Magic IV
army building and economy near-solvable
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.