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 · Practiced Mastery
A Revolution-era Paris entry built around dense crowds and open-ended blackbox assassinations.

Optimization · Practiced Mastery
An accessible action RPG of moral choices, property empires, and a loyal dog.
Assassin's Creed Unity leans Optimization (Practiced Mastery); Fable II leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Unity
Refined parkour, still forgiving combat
Fable II
One-button combat, forgiving by design
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Unity
Co-op partners face scripted guards
Fable II
Scripted opposition
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Unity
Fixed sandbox assassinations
Fable II
Fixed world with minor loot rolls
Fable II leans a little harder on optimization, though the gap is small.
Assassin's Creed Unity
Gear builds and blackbox approach planning
Fable II
Property empire and job economy trivially exploitable
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.