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 · Pure Mechanics
Keeping speed through destruction-racing chaos that punishes clean-lap plans.

Execution · Twitch Chaos
Kart racing where driving skill fights a steady drizzle of random gag items.
FlatOut: Ultimate Carnage leans Execution (Pure Mechanics); Looney Tunes: Space Race leans Execution (Twitch Chaos).
FlatOut: Ultimate Carnage leans a little harder on execution, though the gap is small.
FlatOut: Ultimate Carnage
Holding racing lines through wrecks and ragdoll chaos tests hands
Looney Tunes: Space Race
Racing lines and drift control still decide most finishes
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
FlatOut: Ultimate Carnage
Rival drivers ram predictably, light multiplayer jockeying
Looney Tunes: Space Race
Light gag-timing duels against human racers
Looney Tunes: Space Race leans a little harder on variance, though the gap is small.
FlatOut: Ultimate Carnage
Debris and pileups scramble any planned lap
Looney Tunes: Space Race
Random gag pickups scramble race outcomes
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
FlatOut: Ultimate Carnage
Car upgrades and track shortcuts are mappable
Looney Tunes: Space Race
Shortcut and track knowledge compound every lap
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.