head to head
Helldivers 2 asks more than Rain World, and the gap is optimization.

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

Variance · Twitch Chaos
A brutal survival platformer where you are prey in a living, indifferent ecosystem.
Helldivers 2 leans Optimization (Practiced Mastery); Rain World leans Variance (Twitch Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Helldivers 2
Recoil, stratagem inputs, friendly-fire aim
Rain World
Momentum-based movement and spear throws are slippery and demanding
Helldivers 2 leans a little harder on reads, though the gap is small.
Helldivers 2
Enemies scripted, no adaptive opponent
Rain World
Predator AI is dynamic simulation, not modeling of you
Rain World leans a little harder on variance, though the gap is small.
Helldivers 2
Patrol spawns and modifiers shake missions
Rain World
Creature placement and behavior shift unpredictably each cycle
Helldivers 2 leans clearly harder on optimization.
Helldivers 2
Loadout and stratagem synergies deep
Rain World
Route knowledge and ecosystem mastery slowly tame the chaos
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.