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 · Pure Optimization
A 2D sandbox of procedurally generated planets driven by crafting progression.

Optimization · Systems & Chaos
A lighter loot ARPG of frontier adventurers with class relics and buildable forts.
Starbound leans Optimization (Pure Optimization); Torchlight III leans Optimization (Systems & Chaos).
Starbound leans a little harder on execution, though the gap is small.
Starbound
Light platforming and combat, generous margins
Torchlight III
Simple skill rotation and dodging
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Starbound
Procedural NPCs follow simple fixed behaviours
Torchlight III
Monsters are scripted fodder
Torchlight III leans a little harder on variance, though the gap is small.
Starbound
Procedural planets and loot keep early exploration unknown
Torchlight III
Loot and map randomness standard for genre
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Starbound
Gear tiers, farming, and progression routes dominate
Torchlight III
Relic and skill builds, fort crafting bonuses
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.