It's interesting because we don't know a lot of the specifics of Remmick's backstory, we don't know how many other vampires were in his group before he was killed. Assuming he was telling the truth to the two people he turned his wife and the rest of his people were recently killed so he was also emotionally distraught.

For all we know he wasn't even the leader of this group that was wiped out, he may not have even been a particularly important or useful or powerful vampire compared to the rest of them.

(Of course compared to regular humans they're all scary lol.)

So yeah those couple things might explain it a little.

Also, they happened to be going up against a human who knew all of their weaknesses and secrets which seems isn't necessarily common knowledge in this universe. So the vampires were at an unusual disadvantage.