I personally don't find it "remarkably heavy." Kind of a funny thing to say, when you figure we are talking about a mouse. lol I agree in regards to I guess a DA, it does have more weight to it. I personally, like the weight it has.
Also if you really look at a mamba up close the grip you have on the sides is different then the DA. The thumb area for example, has this rubber groove that slopes inward, the DA just goes down flat. On the pinky side of the Mamba, you have another rubber coated groove that cuts in-ward. Makes it a bit more narrow at the base. Those slight adjustments make the mouse really comfortable for me.
The overall feel of the mouse seems to be made of higher quality materials. You also notice the base of the Mamba has this thick see-through smoke tinted type plastic. Where the DA base just has that piano gloss plastic.
Then you have the fact that its Wireless. Which I have really started to like a ton. its something you think isn't a big deal. But after you spend sometime with it, its def nice. So basically your getting a DA with a slightly varied shape, wireless, and has more weight. The con you give up is when you lift off, the cursor jumps more then it does with a DA. On pad tracking though, they don't differ all that much.
If you prefer a lighter mouse and want to keep wired then the DA is def one of the top mice around. I feel that with the extra features the mamba has it works great for me on a personal level. However, I will say my 1800DPI DA has the best tracking performance out of any of the mice I own and if I where to play professional gaming, I would go with that. But I just sit at home and play for fun, so I can sacrifice on pure performance and gain in the areas that I see fit. I feel people stress over mouse and keyboard way to much. Unless your getting paid to play the majority of stuff out there is fine. And even in the case where you are a pro, they usually get stuck using products from whoever sponsors them. So it just goes to show, you can make whatever work.