If all that holds all of metal together as a genre is the agreement on using guitar, bass, and drums, then what makes it metal and not just jazz or rock or any other genre that likes to depend on those instruments?
To me, the most important, basic thing going on with Hessian.org and the DLA and the kind of metal analysis that goes on around here is the attempt to look for that something else that is often very difficult to articulate that is behind why these bands seem to us to hang together so well in this broad category "metal". The more you start to try to differentiate the genre and decide what makes metal metal, the more you find yourself building into it and before long you're talking about alot of things you might not have thought would go into it at first glance like attitude and values.
The more features that are drawn out in this manner, the more discerning the eye for genre distinction and genre quality. Is this worth doing or is it just a bunch of wasted breath and overanalysis? Undoubtedly it can be taken too far, but at the same time, I think issues of genre quality are important. For example, we want to be able to say more about why 1,385,238 bedroom black metal bands are so awful than merely that we dislike them or think they suck. It would be nice to be able to articulate some reasons that are justified by some more in-depth standardized categories.