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 · Practiced Mastery
Precise shot aiming plus planning the run-out several balls ahead.

Execution · Practiced Mastery
Simulation driving precision underpinned by setup tuning and race strategy.
8 Ball Pool leans Execution (Practiced Mastery); Project CARS leans Execution (Practiced Mastery).
Project CARS leans a little harder on execution, though the gap is small.
8 Ball Pool
A perfect aim-line cheat wins nearly every rack outright
Project CARS
Braking points and wheel control at the sim limit
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
8 Ball Pool
Opponents alternate turns; little adaptive interaction to predict
Project CARS
Online racecraft against humans adds light positional prediction
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
8 Ball Pool
Break spreads add some randomness to each rack
Project CARS
Dynamic weather injects some session randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
8 Ball Pool
Position play and run-out planning separate good players
Project CARS
Setup tuning and pit strategy reward deep study
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.