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
First-person puzzle adventure unraveling a Lovecraft-tinged island mystery.

Optimization · Pure Optimization
Balancing town supply chains against mine logistics in a solvable economy.
Call of the Sea leans Optimization (Pure Optimization); SteamWorld Build 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.
Call of the Sea
Walking and clicking, no dexterity test
SteamWorld Build
Placing buildings has no dexterity component
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of the Sea
No opponent of any kind
SteamWorld Build
Creature attacks are scripted waves, not an adapting mind
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of the Sea
Hidden solutions surprise only once
SteamWorld Build
Resource layout below ground is unknown until dug
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Call of the Sea
Deducing fixed puzzle logic is the whole game
SteamWorld Build
Supply chains, citizen needs and mine logistics are the entire test
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.