machineelf
Explorer
These things nearly wiped the party, and would have if it wasn't for the cleric turning undead, reviving the downed PCs and retreating.
Sounds like the perfect level of difficulty to me.

I hear a lot of people say that characters are too hard to challenge in 5th edition. That's certainly not true in the first three or so levels. And I find that if you play the NPC monsters viciously and smartly, then it's pretty easy to challenge player characters in all levels.
Anyway, it seems like the encounter was appropriate and you ran it well.