Then why discuss Metallica at all? Or Iron Maiden? If they're such irrelevant jokes today, why bother talking about them at all?
To tell the truth, they both draw large audiences - STILL - and their live shows are still worth every buck. It's hard to compare when they were fresh young guys reeking of diapers to the grown up and calloused musicians of today... and still be fair. In that we agree.
As for Megadeth, they're still around and I hold them in the same high regard as I do Metallica. If I'm not mistaken - please correct me if I'm wrong, as I'm usually wrong - Megadeth endorses the Mayhem fest (or something like it).
The difference from when they became big to now is that the internet and downloading changed the whole thing, but you already know that and I'm being redundant by saying it.
It made it more complicated, with more hands in the pie, more laws and more lawyers, and Metallica showed difficulty in adapting to that kind of situation, I think. Truly protective of their shit, that lot.
If the main interest of all bands concerned was to make shitloads of money by selling records once hitting mainstream, now it can't be that way anymore. It's the live shows that make the cash and it's where these bands still excel - thus drawing thousands.
Stuff from IM's Dance of Death may sound contrived to you, but if you check YouTube you will see it works fine with a large audience.
Sorry. I don't seem to recall anyone complaining about old Metallica.
Look at your calendar (while you decide if you have "a nut" or not) and I hope you notice that this was almost 30 YEARS ago now! FFS! Metallica of new is like Maiden of new. Both are pure jokes.
Sadly, though, I can't come up with any American band that did have more influence on metal. "DID" being the key word.