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.

Execution · Pure Mechanics
Memorising brutal scripted patterns and executing them without a single slip.

Execution · Practiced Mastery
A precision metroidvania about learning fixed boss patterns and tight platforming.
Contra: Hard Corps leans Execution (Pure Mechanics); Hollow Knight leans Execution (Practiced Mastery).
Contra: Hard Corps leans a little harder on execution, though the gap is small.
Contra: Hard Corps
One-hit deaths under relentless bullet pressure demand perfect inputs
Hollow Knight
Precise platforming and pogo timing dominate hard content.
Hollow Knight leans a little harder on reads, though the gap is small.
Contra: Hard Corps
Bosses are fully scripted setpieces
Hollow Knight
Bosses run scripted attack pools; not adaptive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Contra: Hard Corps
Everything fixed once routes and patterns are known
Hollow Knight
Negligible; world layout is fixed.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Contra: Hard Corps
Memorising boss patterns, weapons and branching routes is mandatory
Hollow Knight
Charm builds and boss routes are fully learnable.
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.