If Sabbath isn't metal, then neither is Iron Maiden.
Now Slayer, Sepultura, Obituary, Napalm Death, Cannibal Corpse, Deicide, Carcass, Entombed, Death, Bolt Thrower and Morbid Angel... bands like them, now that's real metal.
He was right. Metal is about soaring vocals and guitar (and some times drum) pyrotechnics. Sabbath had neither, though they were pioneers in very heavy blues-based hard rock. Zeppelin had the vox but Page is a sloppy player. Deep Purple could have been deemed metal, but there was way too much outstanding and tight bluesy playing (every car sold on the planet should play Highway Star on the sound system when the car breaches 88mph). Mötorhead stood alone.
Metal today is almost totally detached from yesterday's metal. Today's metal is mostly screaming or Cookie Monster vocals, a double bass drum ostinato-fest, and guitarists playing many notes and little music. A massive exception to that generalization is Meshuggah, who are brutal AND musical.
Maiden still puts out new and fresh albums with excellent material, everyone in the band can still play (though they're aren't at the same BPM on some songs), their live shows never disappoint (though their Jones Beach show in 2012 was fair at best, and opener Alice Cooper won that day), and they're not on TMZ.
And while this isn't a political post, when I saw Maiden this tour Dickinson acknowledged the differences and fracturing in the world and across nations but stated unabashedly that Maiden fans "are all brothers." It wasn't a left or right thing. No wokism. No bashing Deplorables. It was the most unifying thing I've heard from an entertainer in ages.
....though Bruce also said Maiden unleashed covid on the world...."yeah that was us."