I got into the same discussion with my nephew. Actually he was saying that Khabib is "THE" GOAT.
He said the same thing - "Khabib is 27-0." I told him that's cause Khabib has beat a bunch of nobodies, who don't even have a Wikipedia pages and that even the Leagues he fought in predominantly don't even have a Wiki page. He said "Yea but that was before he was in the UFC." I told him that beating a bunch of nobodies does not get you GOAT statues and then showed him BJ's record. I showed him that BJ **DEBUTED** in the UFC and doesn't have 15 fights from unknown Jabronis (BJ has one guy that doesn't have a Wiki page). He started to get mad cause his "flavor of the month GOAT" argument just got destroyed.
I then showed him several recent pages from MMA sites that listed the top LW GOATS and Khabib was never on top and that BJ always was.
BJ was not even fighting 3 years, moved up and beat Matt Hughes for the first time while Hughes was the UNDISPUTED Welterweight GOAT and in his prime. In the same time period Khabib was fighting Ali "Who Da fuck is Dat Guy" Bagov to a decision in some Jabroni league called Golden "Who Da fuck is Dat Promotion " Fist Russia. If Khabib had moved up, fought and beat GSP when he was in his prime, then this would have been a "BJ Penn Level" accomplishment.
BJ was in Title fights less than a year after his MMA debut. BJ (who is a 145lb fighter) fought a close decision lose to GSP (some say he won), fought to a decision with (future) LHW Champ Lyoto Machida at what would be considered Heavyweight. BJ is a two division champ. BJ has 5 victories over UFC/Pride champs (and a few other minor promotion like Shooto, Hero's) and all of them are in higher weight classes than what he is in now. Two of them were Welterweight champs which is two divisions higher up. Khabib has 2 and 1 of those was a Champ from a LOWER weight class and zero from champs at a higher weight class. BJ's first belt was won by beating THE WW GOAT, while Khabib beat 11th ranked(?) Al Iaquinta on pretty mucha gimme fight. Hell so many more accomplishments for Penn.
Yes his star went out some time around 2009, but if you compare Penn's first 8 years to Khabib's ENTIRE career, there is no comparison. Can Khabib surpass BJ? Who knows, but as of right now Penn's accomplishments are way better.
Hawai`i > Dagestan