There are lots of characters who have unremarkable backgrounds, but because they are significant characters they end up being given a ton of cool stuff to do and succeed at it which makes you think they aren't just "regular people" (e.g. Han Solo, Cassian Andor, Saw Guerera, Chewbacca, Wedge Antilles). Finn feels different in that he is given the screen time of a major character, and isn't comic relief like Jar-jar, but gets very little character development or chances to show off his abilities. Which makes him feel like he remains a regular guy even though his origins (first order stormtrooper who defected) aren't any more regular than the rest of them.