Kaos, I hope you know I don't say this to argue with you but only to offer a slightly different take (and this was really formed for me while watching "Some Kind of Monster" which is, with the possible exception of the Rush doc, my favorite musical documentary ever)...
I think they are the one band that DIDN'T do that. They follow their muse. I respectfully, but honestly, think that the people that think Metallica sold out are those that are wishing for RtL Part 9. Or MoP over and over again. We forget, because it landed, and landed BIG, but The Black Album was a huge risk. They spent a LOT of time on that, and what, remixed it twice or some shit? If it tanked, they were arguably done. Load and Reload were - for them - WAY off the reservation, and there was no guarantee of financial success. St. Anger was more polarizing than any album from Testament, Megadeth, Anthrax, and Slayer COMBINED. Those other bands (with the exception of Testament, who I am not that familiar with) are still doing the same shtick. Slayer is to me a cartoon. Every time I hear them I hear the melody of "Entrance of the Gladiators" (the "circus theme") in my head.
I think if they were really about the "business" first, they would have put out "The Black Puppets", "Load the Lightning", "Reload the Lightning", "St. Justice", "Death Days Revisited", and "Hardwired... to Kill Em All". At least with Metallica (like Zeppelin), if I want to bang heads, I have an album or two to go to. If I want to put a little "prog" in my metal, I have an album to go to. If I want a little classic rock, I have an album to go to.
I think they are way bigger than any of the other bands you mentioned (perhaps, again, combined) and so there is an element to business that is unavoidable. You can't play stadia without at least ONE eye on the wallet, but in that context, in my opinion, they have stayed very relevant and have taken some big risks.