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

Execution · Practiced Mastery
Fan-built ground-up remake of Half-Life with a reimagined Xen.

Execution · Practiced Mastery
Helicopter handling under fire while routing fuel and ammo across fixed missions.
Black Mesa leans Execution (Practiced Mastery); Desert Strike: Return to the Gulf leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Black Mesa
Classic FPS aim and platforming sequences
Desert Strike: Return to the Gulf
Helicopter inertia and dodging fire demand real stick control
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Black Mesa
Marines and aliens follow set scripts
Desert Strike: Return to the Gulf
Defenses are fixed emplacements, nothing adapts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Black Mesa
Minor enemy placement surprises first run
Desert Strike: Return to the Gulf
Maps are unknown on first sortie only
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Black Mesa
Route, resource, and encounter knowledge
Desert Strike: Return to the Gulf
Fuel, ammo and mission-order routing is the strategic core
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.