New player question about Astrology

[Semirhage]

Tank should die so some random healer they'll likely never see again can improve?

Counterpoint: Death in this game is that much of a setback? Your durability loss results in adding something like 20 gil to your repair bill. If the healer isn't that great, that's one thing. If it's a skilled healer on top of their health chicken game, "oops, sorry about that" and everyone's fine.