head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Optimization · Systems & Chaos
Loot-shooter RPG built on gear chasing.

Variance · Systems & Chaos
A twin-stick roguelike won by recognizing which item combinations break the game.
Borderlands 2 leans Optimization (Systems & Chaos); The Binding of Isaac: Rebirth leans Variance (Systems & Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Borderlands 2
Aim matters but generous hit feel
The Binding of Isaac: Rebirth
Twin-stick aim and dodging matter but pace is forgiving.
Borderlands 2 leans a little harder on reads, though the gap is small.
Borderlands 2
Enemies are scripted loot fodder
The Binding of Isaac: Rebirth
Enemies and bosses scripted; no adaptive opponent.
The Binding of Isaac: Rebirth leans a little harder on variance, though the gap is small.
Borderlands 2
Procedurally generated weapon drops vary
The Binding of Isaac: Rebirth
Item pools and room generation drive run identity.
Borderlands 2 leans a little harder on optimization, though the gap is small.
Borderlands 2
Skill trees and gear math heavily solved
The Binding of Isaac: Rebirth
Item synergy knowledge defines whether runs snowball.
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.