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.

Optimization · Practiced Mastery
Top-tier co-op shooter against bug and bot hordes.

Execution · Twitch Chaos
A kart racer where item luck collides with optimized lines and builds.
Helldivers 2 leans Optimization (Practiced Mastery); Mario Kart 8 Deluxe leans Execution (Twitch Chaos).
Mario Kart 8 Deluxe leans a little harder on execution, though the gap is small.
Helldivers 2
Recoil, stratagem inputs, friendly-fire aim
Mario Kart 8 Deluxe
Drift boosts, snaking, and item timing demand precision.
Mario Kart 8 Deluxe leans a little harder on reads, though the gap is small.
Helldivers 2
Enemies scripted, no adaptive opponent
Mario Kart 8 Deluxe
Human racers bait and block items but mostly reactive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Helldivers 2
Patrol spawns and modifiers shake missions
Mario Kart 8 Deluxe
Item distribution heavily randomized by position.
Helldivers 2 leans a little harder on optimization, though the gap is small.
Helldivers 2
Loadout and stratagem synergies deep
Mario Kart 8 Deluxe
Kart build, line, and shortcut knowledge define top times.
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.