head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
Scheduling scarce time and resources across a base run by copies of yourself.

Optimization · Pure Optimization
Mastering faithful D&D 3.5 rules and party builds against dice-roll swing.
The Alters leans Optimization (Pure Optimization); The Temple of Elemental Evil leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
The Alters
Third-person walking and menus, no twitch demands
The Temple of Elemental Evil
Turn-based clicks - hands never matter
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
The Alters
No adaptive opponent, only systems and story beats
The Temple of Elemental Evil
Encounters run on D&D scripts, not adaptation
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
The Alters
Unscouted events and alter reactions surprise first runs
The Temple of Elemental Evil
Dice rolls swing fights until builds overpower them
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
The Alters
Time, resource and crew scheduling under deadlines is the game
The Temple of Elemental Evil
Mastering 3.5e rules, builds and positioning is the game
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.