Maybe this encounter was a little overturned, eh?

Balancing encounters is for scrubs. Fair fights are for losers.

One of the things I learned from being in a group that rotated DMs: Some DMs really expect more or different things from players tactically.

Like, when one guy was running you could pretty much just run into a room and fight, and you'd win. You'd have plenty of time to long rest, so you should just blow all your spells.

The other guy expected like some scouting and planning. Take out the outer patrols first without letting them get a message to the castle, then assault the warlord. Going directly in means you'll be flanked by those patrols. The total size of what you'll be dealing with is pretty well known, so you can ration your spells out with pretty good information.

And then there's the "This dungeon is inhabited intelligent creatures that have spent years fortifying it against intrusion. You don't know the layout or what forces you'll face. Your enemies are advancing their goals, and every day you spend means more of your homeland is consumed by The Dirge"

I'm between #2 and #3 there. The wizard struggled a little going from "leveled spell every round" to "I should think about my resources."

I still tend to run things a little too hard, but the group I ran for full time got into the groove and never wiped.