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

Optimization · Practiced Mastery
A strategy shooter testing defense placement economy backed by active gunplay.

Optimization · Pure Optimization
Side-on turn-based tactics where you manually aim ricocheting bullets for a steambot pirate crew.
Fortified leans Optimization (Practiced Mastery); SteamWorld Heist leans Optimization (Pure Optimization).
Fortified leans a little harder on execution, though the gap is small.
Fortified
Third-person shooting between waves keeps hands busy
SteamWorld Heist
Manual aim and ricochet shots reward steady hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fortified
Martian waves are scripted compositions
SteamWorld Heist
Enemy bots follow fixed behaviors
SteamWorld Heist leans a little harder on variance, though the gap is small.
Fortified
Wave makeup is known after a single attempt
SteamWorld Heist
Procedural ship layouts and loot drops
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fortified
Defense placement and hero loadout economy decide rounds
SteamWorld Heist
Crew builds, weapon picks, and turn routing carry runs
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.