head to head
Grand Theft Auto V asks more than Assassin's Creed Syndicate, and the gap is reads.

Optimization · Practiced Mastery
Twin assassins seize Victorian London borough by borough with gang warfare and a rope launcher.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Assassin's Creed Syndicate leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Assassin's Creed Syndicate
Rope-launcher traversal and simple brawling
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Assassin's Creed Syndicate
Gangs are scripted
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Assassin's Creed Syndicate
Fixed activities
Grand Theft Auto V
Some mission and lobby randomness.
Assassin's Creed Syndicate leans a little harder on optimization, though the gap is small.
Assassin's Creed Syndicate
Gang upgrades and borough takeover planning
Grand Theft Auto V
Heists, money loops, builds learnable.
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.