Aquaman (Post-Crisis) vs Ruin Athe: who would win?

Ruin Athe favored — Slight edge (~55%)

Aquaman (Post-Crisis) · DC · Base

Tier
3-C, up to LOW 1-C
Attack Potency
Galaxy Level, up to Low Complex Multiverse Level
Speed
Hypersonic, up to Massively Ftl+
Durability
Galaxy Level, up to Low Complex Multiverse Level

Ruin Athe · Saint Seiya · Base

Tier
3-C, up to LOW 2-C
Attack Potency
Galaxy Level, up to Universe Level+
Speed
Speed Of Light
Durability
Galaxy Level, up to Universe Level+

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.