head to head
Neither is simply harder - they are hard in different places. F1 Race Stars demands more reads; Mario Kart 8 demands more variance.

Execution · Twitch Chaos
Kart-racing control with item RNG swinging family-friendly races.

Execution · Twitch Chaos
A kart racer where controlled chaos from random items tempers otherwise precise driving skill.
F1 Race Stars leans Execution (Twitch Chaos); Mario Kart 8 leans Execution (Twitch Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
F1 Race Stars
Kart handling and boost timing decide clean laps
Mario Kart 8
precise drifting and item timing matter
F1 Race Stars leans clearly harder on reads.
F1 Race Stars
Human racers feint and time item attacks in multiplayer
Mario Kart 8
minimal, mostly reacting not predicting
Mario Kart 8 leans clearly harder on variance.
F1 Race Stars
Item rolls swing positions like any kart racer
Mario Kart 8
item boxes are heavily randomized
Mario Kart 8 leans clearly harder on optimization.
F1 Race Stars
Track shortcuts and KERS timing are learnable edges
Mario Kart 8
track lines and item strategy solvable
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.