Hey there. Thrillmonger actually needs 40 final blows on non-guardian enemies. The end of match stats will count assist kills, which do not count towards Thrillmonger.
I got one during my last bout of Gambit'ing -> https://destinytracker.com/destiny-2/pgcr/9465398452
D2Tracker shows the medals earned if you click on a player's name. (My death was during the Primeval phase after I'd earned the medal). It is definitely still earnable.
Is there a match where you believe you should have earned it? Look up the PCGR on D2Tracker.
I have multiple games where I counted physically, but if there is some type of glitch hasn't given it to me then maybe that's why I'm short some how...
Hey there. Some of the ones you yourself counted might have been assists rather than final blows. Like EckyThump mentioned above, you’ll have to link us a PGCR that has the correct number of defeated enemies where you feel you should have been awarded the medal but were not.
(Like EckyThump mentioned, I have also gotten some thrillmonger medals recently, so anecdotally i can say the medal is obtainable.)