Altaïr Ibn-La'Ahad vs Gary Mitchell: who would win?

Altaïr Ibn-La'Ahad favored — Slight edge (~55%)

Altaïr Ibn-La'Ahad · Assassin's Creed · Age 24-63

Tier
9-A
Attack Potency
Small Building Level+
Speed
Subsonic, up to Supersonic+
Durability
Small Building Level+

Gary Mitchell · Star Trek · Base

Tier
8-C, up to HIGH 6-A
Attack Potency
Athlete Level, up to Multi-Continent Level
Speed
Athletic Human, up to Massively Hypersonic+
Durability
Building Level, up to Multi-Continent Level

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