I still think they class as hardcore, and the two often sit side by side. When I declared this thread an appreciation of metal, that also includes hardcore, and industrial, and goth, and even just honest-to-goodness hard rock. Cave In have indeed gotten less heavy with every record, but I agree with you that it's a good thing. I'd also say they're still metal enough to fit into this picture, as are bands like Favez, Rival Schools and Jimmy Eat World. Yes, they're not strictly "metal", but it's the same umbrella; loud, guitar-led, emotional music.
freylis,can cave in really be put under the metal genre of music any more?
And yea, Avenged Sevenfold do indeed shred. Much better than the similarly-styled Killswitch Engage as well.