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Genres are labels, not purity tests
Stop asking "is this really metal?" Ask which records and scenes it sits next to.
Genre tags exist because listeners need drawers. The drawers help. Purity tests do not.
Rough map: blues and rock & roll supply the basic riff vocabulary. Psychedelic stretches form and studio tricks. Prog keeps long structures and odd meters. Hard rock turns amps up and keeps songs relatively direct. Metal tightens rules, speed, and tone. Punk cuts length and technique; post-punk puts atmosphere and art-school methods back in. Grunge mixes punk dynamics with heavy riffs. Britpop puts UK guitar bands back on the charts. Indie is a shifting umbrella for non-major, guitar-led scenes.
Bands that sit between tags—Radiohead, The Clash, Tame Impala—are normal. Scenes leak.
Use the Genre Map as orientation, not a courtroom. Branched means a sub-style left the parent. Influenced means borrowing. Fused means two families mix on the same record. If two tags conflict, play the landmark track on the band page and decide with your ears.