I haven't seen that, there's one on this page exactly about Finn being a trained soldier, but this prompt explores him as what he says, a trooper working in sanitation. If he was the elite in canon (which doesn't matter much if all the OP did was watch the movie) then there's some flaws in the thinking of Finn as a character as a whole. If the massacre which he refused to take part in was his first mission, then why would Phasma have him as her protege? He clearly wasn't up for the job. Even though he was a quick study with Poe during his escape, he should have obviously shown signs of dissent earlier in his training. And let's be clear here, his proficiency isn't something to be proud of, he's not there by choice. He was taken. He's was/is a child soldier, so let's not make him out to be some hero of justice in the first order.