I think he gets a bad rap really. Holloway, Alvarez, Gaethje and Pettis are all great wins, then he has a bunch of good wins against CDF, Miller, stopping the very difficult to finish Bobby Green.
Its not about him getting a bad rap, hes a great fighter but I just don't think he's really proven himself to the point of being able to claim he's one of the GOAT in the division.
Alvarez is obviously a great win, I myself rank him among the GOAT.
Gaethje is good, I believe he was ranked at the time.
Pettis was 7-5 in the UFC when he lost to Poirier and had lost 4 of his last 6 at the time so already past his best days though might've still been ranked(would've been undeserved IMO).
Holloway is unproven at LW, though to be fair Poirier's win was an upset.
Miller was on a 3 fight win streak but not ranked so a good but not great win, definitely past his best days when he was on the cusp of a title shot.
Green was coming off a loss though still ranked so decent win.
CDF was coming off a loss and was only 2-1 in the UFC, hadn't quite hit his stride.
Not trying to shit on Poirier. He's had a pretty good run at LW with solid competition, none of those guys are scrubs. But as of now he doesn't really have the kind of wins to rank him among the GOAT at LW. I'll say in his defense if you combine his FW and LW career he does have quite the resume, being a consistent contender in two of the toughest division in the sport is no easy feat. But he's far from the GOAT conversation at either weight class based on his accomplishments within each.