Tsunade gets a free pass IMO since she's meant to be this vain old lady, living in a young prime body. Of course she'd give herself gigantic breasts too. Similarly Hinata and Mei keep it under control too. Can you imagine if we saw Sakura or Hinata in this pose? It just doesn't work.
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Not only does it devalue your character but Fairy Tail wastes panel time and forces horny pre-teen comedy, taking us OUT of the actual story.
It'd be like Kill la Kill and us not being able to respect or fear our main characters. Because their tits are always out.