Finn was way more comedic in TFA. the fact it didn’t go anywhere, again, can only be laid at Abrams’ feet. TLJ is where he became a person beyond those trailer moments. Poe was never even meant to be a main character, TLJ gave him an arc to make him into a character, but Poe surviving the crash in TFA is a big part of why Finn gets sidelined later on: the two characters are too similar.
He has an impact in TLJ. Just because that impact is a failed plan (to disable the hyperspace tracking) does not mean it didn’t have an impact. Had they not gone on that mission, with Poe’s blessing, Holdo’s plan to escape to Crait would’ve worked. The Canto Bight sequence is immensely relevant to the story.