Billy Kid vs Bastion: who would win?

Billy Kid favored — Slight edge (~55%)

Billy Kid · Zenless Zone Zero · Base

Tier
8-C
Attack Potency
Building Level
Speed
Superhuman, up to Massively Hypersonic
Durability
Building Level

Bastion · Overwatch · Overwatch 1

Tier
8-C, up to HIGH 8-C
Attack Potency
Building Level, up to Large Building Level
Speed
Immobile, up to Hypersonic+
Durability
Building Level, up to Large Building Level

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