Making Finn a janitor was one of those things that was played for a cheap laugh without actually thinking of all the ramifications it would have on the story; poor screenwriting.
Sure if you ignore the fact that he was also still a full fledged storm trooper.
A full fledged storm trooper with no combat experience. Anyway none of this changes what I or rcaido said. How is a ex-janitor taking out
"a 6ft 7 super armor bitch"and how is Finn being [in sanitation] add anything to the story besides a cheap laugh; it doesn't even have a pay-off like they get stuck in a trash compactor or something.
Also because the movie puts humor over storytelling we the audience is left speculating how a guy goes from cleaning toilets to one of Kylo Ren's personal escorts.