head to head
Destiny 2 asks more than Diablo III, and the gap is execution.

Optimization · Practiced Mastery
A looter shooter where build optimization gates raid and seasonal content.

Optimization · Pure Optimization
A pure loot-and-build treadmill where set-bonus optimisation and Rift pushing define performance.
Destiny 2 leans Optimization (Practiced Mastery); Diablo III leans Optimization (Pure Optimization).
Destiny 2 leans clearly harder on execution.
Destiny 2
Gunplay matters but raids forgive mechanics.
Diablo III
Greater Rift pushing has minor mechanical demand in builds
Destiny 2 leans a little harder on reads, though the gap is small.
Destiny 2
PvE is scripted; Crucible has light adaptation.
Diablo III
No meaningful adaptive opponent; co-op is cooperative
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Destiny 2
Loot drops and rolls drive the chase.
Diablo III
Primal Ancient drops and set dungeon RNG drive the grind
Diablo III leans a little harder on optimization, though the gap is small.
Destiny 2
Build crafting, mods, and damage rotations dominate.
Diablo III
Set bonuses and paragon levelling are almost entirely solvable
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.