All alchemists have access to the same cantrips and 1st level spells (called formula), meaning that all alchemists can create minor damaging effects (ray of frost, poison spray), cure salves (cure wounds), and low-level physical and mystical enhancements.But Frostbite's debuff is much better than Ray of Frost's. So far, it seems like Ray of Frost is a little better. Ray of Frost is a ranged spell attack versus Frostbite being a save or suck cantrip, and Ray of Frost does a d8 of damage versus Frostbite's one d6.
However, it would still stack with other speed reducers like Lance of Lethargy or Frost Lance.