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Anime disregards game stats to present megas differently. All ME's are treated as an upgrade, but all have some outside effect that doesn't happen in-game (emotional bond needs to be strong enough or Cynthia deciding not to furrther push her 'Chomp when it ME'ed the first time vs. literally getting a feebie handout Lucario and being able to ME it in several battles running before going to the pokécentre to heal up, which leaves no lasting effects of battle damage).
M-Chomp probably would have been an upgrade but in the anime world, ME also fucks about with the respective pokémon, like the in-ame lore had said from the outset too.
