head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Twitch Chaos
A kart racer testing drift execution amid item-driven randomness.

Execution · Twitch Chaos
Co-op zombie shooter whose AI Director reshuffles every run to keep teams honest.
Garfield Kart leans Execution (Twitch Chaos); Left 4 Dead leans Execution (Twitch Chaos).
Left 4 Dead leans a little harder on execution, though the gap is small.
Garfield Kart
Drifting and racing lines need precise control
Left 4 Dead
Headshots, melee shoves, and special-infected reaction time
Garfield Kart leans a little harder on reads, though the gap is small.
Garfield Kart
Light multiplayer item-timing prediction against humans
Left 4 Dead
Versus mode adds human ambush mindgames
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Garfield Kart
Random item pickups swing race outcomes
Left 4 Dead
AI Director randomizes hordes, items, and specials
Left 4 Dead leans a little harder on optimization, though the gap is small.
Garfield Kart
Shortcut routing and item management reward planning
Left 4 Dead
Team spacing, route choice, and resource discipline
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.