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 · Pure Optimization
Remake of Gaiden with dual protagonists and explorable dungeons.

Optimization · Pure Optimization
Building a team and exploiting type-matchup math against scripted trainers.
Fire Emblem Echoes: Shadows of Valentia leans Optimization (Pure Optimization); Pokémon LeafGreen Version 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.
Fire Emblem Echoes: Shadows of Valentia
Turn-based menus only
Pokémon LeafGreen Version
Menu-driven turn battles demand no physical skill
Pokémon LeafGreen Version leans a little harder on reads, though the gap is small.
Fire Emblem Echoes: Shadows of Valentia
Scripted enemies on both routes
Pokémon LeafGreen Version
Trainers are scripted; link battles are a side mode
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fire Emblem Echoes: Shadows of Valentia
Hit RNG plus dungeon encounters
Pokémon LeafGreen Version
Wild encounters, catch rolls and crits add mappable RNG
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fire Emblem Echoes: Shadows of Valentia
Dual-army routing and class promotions
Pokémon LeafGreen Version
Type matchups and team building are the solvable core
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.