head to head
FlatOut: Ultimate Carnage asks more than Micro Machines World Series, and the gap is optimization.

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

Execution · Pure Mechanics
Twitchy miniature racing where handling beats strategy on chaotic tabletop tracks.
FlatOut: Ultimate Carnage leans Execution (Pure Mechanics); Micro Machines World Series leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
FlatOut: Ultimate Carnage
Holding racing lines through wrecks and ragdoll chaos tests hands
Micro Machines World Series
Tiny-car handling on cramped tabletop tracks is twitch-heavy
Micro Machines World Series leans a little harder on reads, though the gap is small.
FlatOut: Ultimate Carnage
Rival drivers ram predictably, light multiplayer jockeying
Micro Machines World Series
Human racers can be baited with weapons and blocks
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
FlatOut: Ultimate Carnage
Debris and pileups scramble any planned lap
Micro Machines World Series
Pickup spawns and battle chaos add randomness
FlatOut: Ultimate Carnage leans clearly harder on optimization.
FlatOut: Ultimate Carnage
Car upgrades and track shortcuts are mappable
Micro Machines World Series
Track knowledge is shallow and learned quickly
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.