Yeah, there are many many heavy metal bands that are INCREDIBLY talented and show it in their music. That's hardly a waste of time. I don't know why you think Metallica isn't heavy metal either, they essentially redefined the genre, but while that means they are different, it also means that at the core they're IN that genre. It's like saying the Beatles aren't rock because they changed what rock meant.
Also, you should note that your concept of 14 or 15 year old boys liking metal (implying that they're the primary target audience) is pretty off. Heavy metal listeners are more likely to also like concert music (classical, baroque, opera, etc) than most other types of music. Concert music listeners and heavy metal listeners have a huge crossover demographic, which is why it's actually surprising that something like S&M hasn't been done a LOT by now. I don't have numbers on the demographics, but I'd wager there are much more metal heads in their 20s and 30s than in their early teens (speaking proportionately, as well as total). THis is not to say that metal doesnt' appeal to young teens, but labeling that the primary market or demographic shows a misunderstanding of what heavy metal does both stylistically and technically.