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.

Optimization · Pure Optimization
The genre-defining metroidvania with deep RPG systems.

Optimization · Pure Optimization
Managing clone resources and mapping patrol circuits to chain ghost kills through vertical levels.
Castlevania: Symphony of the Night leans Optimization (Pure Optimization); Styx: Shards of Darkness leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Symphony of the Night
Forgiving action combat
Styx: Shards of Darkness
Climbing and kill-window timing are modest but present demands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Symphony of the Night
Scripted bosses
Styx: Shards of Darkness
Dark Elves and Dwarves use scripted patrol trees throughout
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Symphony of the Night
Item drops and rare gear
Styx: Shards of Darkness
Level geometry is consistent; knowledge transfers cleanly between attempts
Styx: Shards of Darkness leans a little harder on optimization, though the gap is small.
Castlevania: Symphony of the Night
Build crafting and sequence breaks
Styx: Shards of Darkness
Clone economy, rope optimisation, and route planning are the lead skill
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.