Excuse me, sir, but he definitely is. Khabib and Tony #1 and #2, in whichever order you prefer, and Dustin is #3. Who else at 155 beats him?
C'mon now...
Looking at his most recent fights:
KO'd by Michael Johnson - who would probably do it again since Dustin's striking is downright rudimentary, reliant on his power and debatably above average hand speed, while Johnson is quicker and more technical
Won a majority decision against Jim Miller - after they pulled him out of the pyramid and blew the dust off (still mah dude though, even if I REALLY want him to hangem' up...)
Then the Alvarez NC
Beat Pettis - after ol' Tony tried to get out of a [body triangle, I think?] by temporarily relocating his ribs; and who hasn't won 2+ fights in a row in his last 10 fights...
TKO'd Gaethje - a pretty prime match up for Dustin, given his power and Justin's habit of just eating strikes to the head; a quality win though, but not top 5
TKO'd Eddie in the rematch - who, at that point, had 1 win, 1 loss, and 1 NC, and who just got floored in the 1st round of his first OneFC fight a few weeks ago
Now, won a decision over the 145lb champ - who is clearly significantly smaller
I'll take Kevin Lee, Iaquinta, Cerrone, and Barboza as wins over Poirier. Michael Johnson as a "probably". Then, I'll add Gregor Gillespie and Paul Felder as strong 'maybe's over Poirier too.
The dude is chinny and often makes major mistakes in his fights that are wide open for his opponents to take advantage of - he even said that Max, who is obviously MUCH smaller than Dustin and has never packed heavy power in spite of his volume-derived TKOs, had hurt him pretty bad in this fight.
The UFC clearly threw him a bone here with this int(AKA, worthless) title shot, for being a 'company man' - though, I would've preferred to see them toss it to Cowboy instead. Dustin was in the right place at the right time with the right record vs the top 5 who have been fighting each other(while Dustin only fought Eddie when he was top 5, every other opponent being outside); he didn't get this title shot because he "earned" it.