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

Execution · Practiced Mastery
White-knuckle chase driving and route memorisation through punishing scripted missions.

Execution · Practiced Mastery
Top-down aim and kiting against scripted alien swarms with light upgrade planning.
Driv3r leans Execution (Practiced Mastery); Shadowgrounds leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Driv3r
Unforgiving chase driving and clunky on-foot shooting demand control
Shadowgrounds
Kiting alien swarms top-down rewards steady aim and movement
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Driv3r
Pursuers follow fixed AI logic
Shadowgrounds
Aliens charge on simple scripts, never modelling you
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Driv3r
Traffic adds noise to chases, missions are scripted
Shadowgrounds
Ambush triggers are scripted-but-unknown on first playthrough
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Driv3r
Memorising city routes and mission scripts carries completion
Shadowgrounds
Weapon upgrade routing is a light solvable layer
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.