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
Remake of the original Risk of Rain with new survivors and tighter action.

Execution · Twitch Chaos
Dodging under fire while leveraging deep item knowledge against run RNG.
Risk of Rain Returns leans Optimization (Practiced Mastery); The Binding of Isaac: Afterbirth+ leans Execution (Twitch Chaos).
The Binding of Isaac: Afterbirth+ leans a little harder on execution, though the gap is small.
Risk of Rain Returns
Platforming and aiming demand sharper inputs than original.
The Binding of Isaac: Afterbirth+
Dodging bullet patterns while aiming tears is constant
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Risk of Rain Returns
Scripted enemy behaviour throughout.
The Binding of Isaac: Afterbirth+
Enemies are random or scripted, never adaptive
The Binding of Isaac: Afterbirth+ leans a little harder on variance, though the gap is small.
Risk of Rain Returns
Random item pool defines builds run to run.
The Binding of Isaac: Afterbirth+
Item pools, room layouts and pickups define each run
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Risk of Rain Returns
Survivor kits and routing reward optimization.
The Binding of Isaac: Afterbirth+
Encyclopedic item synergy knowledge converts variance into wins
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.