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

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

Optimization · Practiced Mastery
Revenge-driven open-worlder dismantling a sixties crime empire district by district.
Assassin's Creed Unity leans Optimization (Practiced Mastery); Mafia III 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
Mafia III
Stealth takedowns and gunfights
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
Mafia III
Racket guards follow fixed AI
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
Mafia III
Open world is static
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Unity
Gear builds and blackbox approach planning
Mafia III
District takeover loop and underboss assignments
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.