I am a 48 year old metalhead who has seen a ton of shos
nonmetal bands: grateful dead around 40 shows and bob seger around 7
bands over 10 times -maiden , dio (RIP), rush,
bands between 5 and 10 times- slayer, megadeth, symphony x, kreator, testament, anthrax, motorhead, suicidal tendencies, ozzy/sabbath, judas priest, metallica, flotsam and jetsam, mastodon (at festivals, not headliners). there are probably a couple I am forgetting because they aren't my top bands but they play the festivals all of the time.
the list of bands between 2 and 5 times would be too many to list
Besides being old, I live in Phoenix (everybody stops here either before or after LA) and I often do the European festivals over the summer and you can see a ton of shows at a 3 or 4 day festival.