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
Twin assassins seize Victorian London borough by borough with gang warfare and a rope launcher.

Optimization · Practiced Mastery
Following authored stealth-fear sequences with learnable intended solutions.
Assassin's Creed Syndicate leans Optimization (Practiced Mastery); Batman Begins 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 Syndicate
Rope-launcher traversal and simple brawling
Batman Begins
Combat and stealth inputs are forgiving
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Syndicate
Gangs are scripted
Batman Begins
Guards follow scripted fear and patrol patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Syndicate
Fixed activities
Batman Begins
Encounters are staged identically every run
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Assassin's Creed Syndicate
Gang upgrades and borough takeover planning
Batman Begins
Each fear-scripted sequence has an intended solution to find
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.