The Mad Dogs are fairly flat, but I'm not sure if I would call them completely accurate, as accurate might imply analytical/cold, which the Mad Dogs are not. I'm not sure what would constitute accurate since my headphone knowledge is limited, so there you go.
BUT, I do listen to all the metal bands that you've listed, and the Mad Dogs sound wonderful on them. Particularly, the album of your avatar, the MD's sing on "Of Petrichor Weaves Black Noise"; the guitars and drums are weighty and sonorous, everything is well separated, and they can certainly keep up with all the layers that the song presents. The new alpha pads have brought the midrange of the cans forward; I was worried too that the laid-backness would've been an issue but either I don't know what laid-back means, or it hasn't really made an impact on my listening experience.
Detail is certainly not a problem on these cans at all; they're pretty revealing, as on many other albums I can actually hear ugly distortion on electric guitar tracks that I haven't heard on any other headphones (in particular, Alcest)
Here's a picture of their frequency response:
The green are the LCD-2's,
The red are the old dog padded Mad Dogs
and the blue are the new alpha pads they come with.
Do you prefer their sound over that of your B2? I typically like colder sounding cans, but that might be becausethose are the only decent ones that I am familiar with. Maybe a really good laid back can such as this would do me well. If only I had the money to buy one of everything and try it out for myself. *sigh* If only.