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

Execution · Practiced Mastery
An aggressive soulslike about punishing fixed boss patterns with tight dodging.

Execution · Practiced Mastery
A lean souls-like carried by hardened-parry timing and shell selection.
Bloodborne leans Execution (Practiced Mastery); Mortal Shell 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.
Bloodborne
Aggressive dodges and rally timing demand sharp hands.
Mortal Shell
Hardened parry timing demands inputs
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Bloodborne
Bosses follow fixed movesets; no model of you.
Mortal Shell
Scripted bosses
Bloodborne leans a little harder on variance, though the gap is small.
Bloodborne
Chalice dungeon layouts and drops add some randomness.
Mortal Shell
Minor item randomness
Bloodborne leans a little harder on optimization, though the gap is small.
Bloodborne
Builds, weapons, and boss patterns are studyable and solvable.
Mortal Shell
Shell choice and upgrade routing matter
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.