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.

Optimization · Practiced Mastery
Methodically mapping a hostile station where knowledge and routing beat reflexes.

Optimization · Pure Optimization
An open world where build optimisation dissolves every combat challenge.
System Shock leans Optimization (Practiced Mastery); The Elder Scrolls V: Skyrim - Special Edition leans Optimization (Pure Optimization).
System Shock leans a little harder on execution, though the gap is small.
System Shock
Combat and cyberspace ask competent but dated reflexes
The Elder Scrolls V: Skyrim - Special Edition
Combat timing matters little; difficulty bends to your build
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
System Shock
SHODAN's threats are scripted, not an adapting mind
The Elder Scrolls V: Skyrim - Special Edition
Draugr and dragons run scripted AI packages
System Shock leans a little harder on variance, though the gap is small.
System Shock
Citadel's layout and logs are hidden until uncovered
The Elder Scrolls V: Skyrim - Special Edition
Loot rolls and radiant quests add minor mapped randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
System Shock
Inventory, routing and station knowledge solve the game
The Elder Scrolls V: Skyrim - Special Edition
Perk, crafting and stealth-archer loops trivially solve combat
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.