head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
Stacking multi-class abilities and CT tricks to dominate tactically scripted encounters.

Optimization · Pure Optimization
An original RPG system where engagement optimization and passive-stacking theory dominate hard-mode encounters.
Fell Seal: Arbiter's Mark leans Optimization (Pure Optimization); Pillars of Eternity 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.
Fell Seal: Arbiter's Mark
Turn-based; no timing windows whatsoever
Pillars of Eternity
Real-time-with-pause removes all twitch pressure from the player
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fell Seal: Arbiter's Mark
Enemy AI is scripted; fixed job archetypes behave predictably
Pillars of Eternity
All AI opponents use fixed scripted behaviour trees
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fell Seal: Arbiter's Mark
Random encounters and loot add mild variance; counter procs are minor
Pillars of Eternity
Hidden enemy immunities and ability distributions require investigation
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fell Seal: Arbiter's Mark
Multi-class ability transfers and CT manipulation make this near-FFT optimization depth
Pillars of Eternity
Per-encounter ability management and passive stacking define trial-of-iron mastery
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.