head to head
Demon's Souls asks more than Grand Theft Auto V, and the gap is optimization.

Execution · Practiced Mastery
The original Souls game: scripted boss patterns you solve with builds, routes and disciplined execution.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Demon's Souls leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Demon's Souls leans clearly harder on execution.
Demon's Souls
Stamina-timed dodges and parries punish sloppy hands.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Demon's Souls
Invasions exist but bosses are scripted patterns.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Demon's Souls
World tendency and upgrade drops add mild noise.
Grand Theft Auto V
Some mission and lobby randomness.
Demon's Souls leans clearly harder on optimization.
Demon's Souls
Builds, routes and learned movesets are fully solvable.
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.