Is the heart a weak point of a Logia user? That Monet could be killed By Caesar Clown by stabbing its heart looks a bit awkward to me.

I mean, when Monet was cut by Zoro she didn't look to be prepared to properly activate its logia power to receive the cut and she still was able to survive and regenerate, so it's safe to assume that he can instinctively react, or that even if she got damage on her brain, she was still able to avoid it by converting into it's logia element, and it's sure worse to have your brain splitted in two than having your heart stabbed.

Maybe Law's powers made her unable to use her logia powers, but it's clear that any cut part that is under Law's power still can react to its owners will as shown with Kinemon's legs.

Then maybe it's that Logia users cannot convert their heart to their logia element, so that would be a weak point they have.

I'm asking about the possibility of logia users not being able to convert their heart into their element, so it would be another weak point they would have apart from being attacked with haki. I mean, they could also be killed, for example, by stabbing them with a sword where their heart would be, no need of haki to do that. I'm giving those facts as a support for this possibility, so I'd like your opinion if that's really a fact, a possibility, or there's something that makes the possibility I'm telling impossible.
Concerning Monet, she was too terrified by Zoro's killing intent to properly defend herself. When she was cut, you could see her struggling to move in an attempt to put herself back together. She can't and is shivering with a scared and confused expression on her face. Logia powers activate on a mental level, much like Paramecia and Zoan, however Logias rely on their subconscious to activate the power in the even of danger. It's why they can still touch things, when not using it. There are cases when a human can be paralyzed with fear, as was the case of Monet.





Now, for Law, that's actually pretty simple. Law's power creates a field into which he can manipulate all matter as he pleases. So while inside the field, Law had separated the hearts from the user and enclosed them in their own space. It's why they seem to be frozen in ice, which is how the effect is shown.