Why wouldn't you try Mist Form again? The last ability you got before you entered that area. When you're specifically told, stepping on the leaves will give you away. I mean, would you try to jump over them? Right? And the game didn't give you any tutorial prompts to jump over the leaves, but you'd try it anyway because, duh. Right? You're not supposed to step on them.
It isn't as obvious as you make it out to be. Here are a few pointers:
First of all, you actually had to think of using your mist form in the first place, and since stealth sections tend to arbitrarily remove your in-game abilities, that thought doesn't always immediately come to mind. There happens to be an appreciable difference in logic between don't step --> jump and don't step --> turn into mist. It's nowhere near as intuitive.
As for leaving leaves untouched, I'd initially assumed that Dracula's mist form would rustle the leaves as he passed. Simple trial and error did set that straight, of course, but as I said it isn't entirely obvious.
And then there was the matter of Dracula's mist form invisibility. It took me almost half an hour to figure that one out, mostly because the conspicuous red blur Dracula appears as in mist form led me to think that he was entirely visible. I only ended up discovering this by accident, when I'd gotten stuck and caught trying to cross a set of tree roots that inexplicably formed an invisible wall.
Now, I'm not saying this because I consider every gamer to be incapable of figuring a puzzle out on his own. What I'm trying to explain is that Agreus's maze presented us with a rigid, unilaterally solvable puzzle, but without presenting us the necessary elements to solve it. And that, in my book, qualifies as poor design.
And that isn't the only instance of poor design the maze section suffers from -- there's the fact that the area is designed less like a maze and more like one large, linear corridor; there's the camera, which makes the entire process hard to visually keep track of, and which makes aiming daggers at the bells unnecessarily difficult.
There's also the fact that the stealth section is entirely unjustified; and then, of course, there's the fact that you have fight Agreus only a few moments later.
Its not the pinnacle of stealth mechanics by any means, but its certainly not broken either and the rate at which any given individual loses or keeps their calm is not the responsibility of the designers. They don't program for personality types.
That was a figure of speech, you know.