Lamb of God knows how to deliver a fucking killer show and they give me goosebumps every time i see them. Opeth definitely have more song structure skills as well as pure emotion, but Lamb of God definitely has their own notabilities as well. They certainly didnt sell out to attain their status...
It's all interpretation. I've now heard many of Opeth's albums being labeled as potential concept albums. I think it's ridiculous but however the listener would like to interpret them, all the power to em.
I see your point in that instance but I feel that keys are an essential part of Opeth's sound, or at least piano/ mellotron. For example, Outro to Leper Affinity,Weakness, etc.