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

Execution · Practiced Mastery
The fastest mainline Souls, distilling the formula into aggressive boss duels.

Execution · Practiced Mastery
A character action RPG built on tight parry timing against elaborate scripted bosses.
Dark Souls III leans Execution (Practiced Mastery); Stellar Blade 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.
Dark Souls III
fast roll timing against aggressive scripted bosses
Stellar Blade
Parry and perfect-dodge timing windows define the ceiling
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dark Souls III
PvP invasions exist but are optional
Stellar Blade
Bosses run fixed movesets, learnable not adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Dark Souls III
fixed encounters converge after first sight
Stellar Blade
Encounters and loot are static and predictable
Dark Souls III leans a little harder on optimization, though the gap is small.
Dark Souls III
movesets and builds are fully mappable
Stellar Blade
Exospine builds, gear and moveset study reward preparation
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.