Ok, I will make it short and sweet.
For the past 10 years, no one has given a rat's ass about any of these bands performing their own gigs. Ok, maybe Slayer and Megadeth, but only slightly.
The fact that Metallica can sell out any city, anywhere in the world they go kinda invalidates your point. Slayer and Megadeth draw well all over the world also. Anthrax would be only band who isn't really relevant at this time. I've never seen Anthrax so I would like to see them although I'm sure they were better back in their prime. The other three bands all put on great live shows and I would expect no less this time around. There's going to be incentive for each band to try and blow the others off the stage.