head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, 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
The sequel adds minion mounts and an evil empire to corral with your goblin hordes.
Assassin's Creed Unity leans Optimization (Practiced Mastery); Overlord 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
Overlord II
Minion sweeps plus mounts need moderate control
Overlord II leans a little harder on reads, though the gap is small.
Assassin's Creed Unity
Co-op partners face scripted guards
Overlord II
Scripted empire enemies
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
Overlord II
Deterministic encounters
Overlord II leans a little harder on optimization, though the gap is small.
Assassin's Creed Unity
Gear builds and blackbox approach planning
Overlord II
Minion management and domination choices are solvable
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.