Still no matter if you like the shape or not they cannot be called ergonomic as claw gripping your mouse is obviously going to make you more prone to RSI than a mouse where your hand can rest on it.
Ergonomics is a controversial field. I speak as a former physiotherapist/physical therapist. Ergonomics does not mean something is sculpted so you can rest your bones on it. It refers to the science of fitting the environment to the person to allow for the most natural and safe interface with tools, objects, etc.
In general, something that is comfortable and holds your joints at natural resting positions is good, but when that object is needed for an active task, what is the most comfortable at rest may not be the most practical in action. That is one of the reasons why ergonomics is controversial.
Is an ergonomic split keyboard good for everyone. Not a chance. Just ask around here. Works great for some people and actually increases pain for other people (myself included). It all depends on the task at hand, the way you do that task, and your body.
A claw hand grip might not be as extreme as it might sound. It simply means you tend to hold your mouse with bent fingers instead of resting your entire hand across the mouse.
For me personally, a lot of the "ergo" mice are horrible. It might have something to do with the size of my hands and the length of my fingers. I have difficulty holding down the left click buttons on my nicely sculpted Logitech MX mouse at end of a long day. It could also just be that mouse. I suspect with a slight change in the angle of the button, it would solve my problems with it.
I use a diamondback because the shape is easy to grip and so easy to control. A pencil for example isn't very ergonomic, but the it allows you to grip it in a way which gives you a lot of control.
You lost me here. If it's easy to grip and control, what's so bad about it? I actually wouldn't classify a pencil as an easy to grip item. When you're young, they spend a lot of hours training you how to hold your writing instruments. I don't remember going through boot camp for mouse gripping.