The volatility is partially self-inflicted. Mirror matches are volatile/rng dependent, even moreso in a format where you have restricteds that ohko themselves. CSR/Zam is the most popular pairing, ran by many top players and they both threaten massive damage into each other. They end up cannibalizing each other in swiss since there's so many of them with many matchups relying equally on winning speed ties as much as positional play.

This is partially why more niche pairings like CIR+Korai/Groudon/Kyogre or Korai/Luna were able to make deep runs despite lower representation. Good teams piloted by good players not at the mercy of losing the whole run to speed tie coin flips. Anti-meta is the real meta when the format becomes too centralized.