This is starting to really bug me about WotC's adventures. They never reveal what an encounter was actually designed for (making one start to think that there was little to no consideration made, just went for what seemed cool... it can't really be that, but the fact that they're not willing to document the challenge, i.e. Easy, Medium, Hard, Deadly for 4 PCs at Level X, makes it appear that way).
This is a big issue with me. I think a simple fix (one that would at least give a head's up to the DM) would be to include the CR of the NPCs after their type. "Inside the room are six thieves (treat as
Bandits, CR 1/2, led by a Half-Orc mob enforcer named Grunk (treat as
Veteran, CR 2. (I'm writing from work so don't know the actual CRs)
I ran into this several times with Curse of Strahd, where there never is any acknowledgement about the general intent of the encounter, such as the infamous Hag fight that would mop the floor with the players if played correctly, or the encounter with two Iron Golems in a sealed room. I guess the assumption is that you're going through the adventure with the Monster Manual in one hand, your PC character sheets in the other, double-checking the math the whole time and making copious notes on sticky notes and pasting them all around the adventure, and know exactly what the writer was going for.
My issue isn't with the deadliness (or lack thereof) as much as lack of disclosure. If it was marked that said encounter was supposed to be easy/difficult/lethal/etc., it would serve as a head's up for me to take a second look and make my own determination if I wanted to leave that way or make any further preparations.
I ran into this with the Dragon Heist session before last where the PCs tackled the sewer hideout at the end of Chapter One. The Gazer is such an obviously pathetic fight, but I left him in (PCs deserve some easy wins sometimes), but I didn't realize the full lethality of the Intellect Devourer until after the session where the Fighter was stunned by Devour Intellect and asked "How is this cured?".
Would have been nice for the adventure to note that any PCs afflicted with the Devour Intellect ability can only be restored with a Greater Restoration spell. Said spell could be found at X temple for the cost of Y, Renaer Neverember can pull some strings to get someone to cast it once Floon is rescued, etc. Obviously, anyone afflicted by Body Thief is toast.
Instead, the adventure omits discussing the entire tactical strategy of the creature and the DM (in this case, me) has to come up with something on the fly if they've never used these monsters before. Of course, this is exasperated by the fact that the MM description is somewhat coy about how difficult it is to cure the condition.
This is a longer rant than originally intended and I know I'll just have to be more careful about reviewing all fights ahead of time, but dang, it wouldn't kill the designers to add a line or two discussing the intended difficulty and concerns for some fights.