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 · Twitch Chaos
A scarcity-driven aim test under randomised objectives and spawns.

Execution · Practiced Mastery
Tests arcade sports timing in a licensed fantasy sport with swingy Snitch catches.
Contagion leans Execution (Twitch Chaos); Harry Potter: Quidditch World Cup leans Execution (Practiced Mastery).
Contagion leans a little harder on execution, though the gap is small.
Contagion
Deliberate aim with scarce ammo decides zombie encounters
Harry Potter: Quidditch World Cup
Timing passes, tackles and Snitch chases needs moderate dexterity
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Contagion
Hunted mode pits humans against humans; zombies are mindless
Harry Potter: Quidditch World Cup
Versus a friend, faking plays adds light prediction
Contagion leans a little harder on variance, though the gap is small.
Contagion
Randomised objectives, spawns and routes reshape every round
Harry Potter: Quidditch World Cup
Snitch appearances and combo opportunities add swing
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Contagion
Resource discipline and map knowledge carry survival
Harry Potter: Quidditch World Cup
Special move charging and team choice reward system knowledge
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.