Good points! Playing the devil's advocate a bit here, but I can't necessarily agree with your statement that Lamb of God is "maybe" as "big" as Anthrax back in the day. When you say "big", and not "better", I think of album sales and popularity, to which LoG has a ton of right now. "Wrath" was a so-so album, and debuted at #2, which is incredible in today's music scene. True, they're not selling out stadiums or anything, but give them 20 years and I bet they will.
As influential as Slayer? Hell no. Still incredibly important and influential to metal? You betcha. I've always viewed them as the re-incarnation of Pantera, brining back some southern swag and popularity to metal when it died out in the late 90's. They pretty much revitalized american metal, and directly influenced tons of modern "metal" bands, especially in america, in many genres.