head to head
Neither is simply harder - they are hard in different places. Rocket League demands more execution; Wreckfest demands more variance.

Execution · Pure Mechanics
Mechanical car-soccer where execution is the ceiling.

Execution · Pure Mechanics
Demolition derby racer with destructible PvP chaos.
Rocket League leans Execution (Pure Mechanics); Wreckfest leans Execution (Pure Mechanics).
Rocket League leans clearly harder on execution.
Rocket League
Aerials, flicks, dribbles, pure mechanical ceiling
Wreckfest
Demolition driving, ramming angles
Rocket League leans clearly harder on reads.
Rocket League
Rotations and 50-50 reads against humans
Wreckfest
Online derby PvP rewards ramming reads
Wreckfest leans clearly harder on variance.
Rocket League
Almost deterministic physics
Wreckfest
Crash physics chaos
Wreckfest leans a little harder on optimization, though the gap is small.
Rocket League
Training routines, rotation theory
Wreckfest
Car upgrades and durability tuning
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.