Wither Skeleton vs Bastion: who would win?

Wither Skeleton favored — Slight edge (~55%)

Wither Skeleton · Minecraft · Base

Tier

8-C

Attack Potency

Building Level

Speed

Below Average Human, up to Subsonic

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.