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

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

Execution · Pure Mechanics
Tests twitchy miniature car control and track memory amid party-weapon chaos.
FlatOut: Ultimate Carnage leans Execution (Pure Mechanics); Micro Machines V3 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 V3
Tiny cars on twisty tabletops punish every slip
Micro Machines V3 leans a little harder on reads, though the gap is small.
FlatOut: Ultimate Carnage
Rival drivers ram predictably, light multiplayer jockeying
Micro Machines V3
Couch rivals can be baited with weapons and nudges
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 V3
Pickup spawns and chaos shuffle close races
FlatOut: Ultimate Carnage leans a little harder on optimization, though the gap is small.
FlatOut: Ultimate Carnage
Car upgrades and track shortcuts are mappable
Micro Machines V3
Track memorisation and shortcut lines pay off
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.