I agree that trolls, traps, and werewolves have kind of cursed design in this regard. How much of a threat they pose is really tied to what you're allowed to know about them. In games with monster knowledge rules, you can really easily find that the difficult of many encounters boils down to "roll a die, success cuts the challenge in half".
And I like having dedicated monster knowledge rules, but so many classic monsters (and many new ones) seem to be designed with issue. Players walk into encounters predisposed to be wary of statues, beautiful women, and unassuming treasure chests- to the point that many a GM grumbles annoyed that the players are "metagaming", but the situations where the players are right to be cautious keep coming up!
5e claims to be a game where you can run it just like the old school games of old, but the options it gives to players fight against that notion every step of the way. Or alternately, there's too many "old school" challenges cluttering up a game that is designed for a different paradigm. It comes to about the same thing.