Sosrim, Targo, Paddy, and Wilf, skip over this one. This also might have minor CoS spoilers.

I was running CoS a couple of days ago and ran an encounter with a level 4 party where Strahd sent Rahadin, two swarms of bats, and three ghouls to try to get the Tome of Strahd back from the PCs. Their ranger is unfortunately out of town, so it was just a berserker barbarian, a knowledge cleric, and a divination wizard against an encounter that I surely thought they were going to lose. I was trying to design the encounter so that they would put up a decent fight, only to get knocked out so that Rahadin can steal the tome back while Strahd watches from a window.

Instead, the party performed far better than I thought they would. The barbarian and cleric managed to take out both bat swarms while the wizard made good use of web, slowing Rahadin and the ghouls down long enough for the cleric to turn undead, forcing the ghouls to flee and isolating Rahadin.

The party took a beating, and the wizard had to blow a lot of luck dice (he's a halfling divination wizard with the lucky feat) to not get murdered, but eventually they forced a stalemate with clever usage of flaming sphere, lighting the burgomaster's mansion where they were fighting on fire.

Needless to say, I was impressed. That said, the party felt helpless for a lot of the fight, the wizard and cleric seemingly forgetting about how useful their utility spells were (the turn undead/web combo more or less won the fight for them), and the barbarian suffered from really bad rolls (hitting 8s and 6s on reckless attacks with advantage), and even though they won, morale hit the floor, as they barely escaped with their lives but lost the Tome of Strahd in the process.

So, was it too harsh of me to throw an encounter like this at them? How do I get the support casters to realize their role is just as valuable as doing damage? Do you think they'll stop worrying about their lack of damage when the ranger comes back and starts putting up big numbers?

I know this is a little long for this thread, but I didn't want to make a new post for it. Thanks for letting me know your thoughts.