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 kart racer where controlled chaos from random items tempers otherwise precise driving skill.

Execution · Twitch Chaos
A permadeath bullet-hell MMO where dozens of players swarm gods and one mistake erases your character.
Mario Kart 8 leans Execution (Twitch Chaos); Realm of the Mad God leans Execution (Twitch Chaos).
Realm of the Mad God leans a little harder on execution, though the gap is small.
Mario Kart 8
precise drifting and item timing matter
Realm of the Mad God
Dodging dense bullet patterns with permadeath stakes
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Kart 8
minimal, mostly reacting not predicting
Realm of the Mad God
Boss patterns are scripted; other players cooperate, not oppose
Mario Kart 8 leans a little harder on variance, though the gap is small.
Mario Kart 8
item boxes are heavily randomized
Realm of the Mad God
Loot drops and event spawns gamble your character's fate
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Kart 8
track lines and item strategy solvable
Realm of the Mad God
Gear tiers, class knowledge, and dungeon routing compound
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.