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
Piloting skill plus careful fuel and ammo routing across scripted missions.
Black Mesa leans Execution (Practiced Mastery); Nuclear Strike 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
Nuclear Strike
Helicopter piloting and aimed strafing under fire demand steady hands
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
Nuclear Strike
Enemy emplacements follow fixed scripts
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
Nuclear Strike
Map layouts are unknown on first pass 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
Nuclear Strike
Managing fuel, ammo and mission routing is the real layer
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.