At this point in the gamme's life, it just makes sense to have the HW classes unlock at level 30 now. With HW being part of the base game, and all.

AT THE VERY LEAST, AST. Most of the level 30-50 AST quests take place in the Black Shroud. They could have the level 30 quest start with E-Suni-Yan in the CNJ guild at level 30 (whether or not you've finished the CNJ quests/unlocked the WHM Job Stone quest), he sends you down to South Shroud to investigate "Whispers from the Elementals of travelers from afar" or some such. Then from level 30-50, the AST questgivers post up in the CNJ guild, moving to Ishgard once you complete the level 50 quest.

This would be a way more logical progression, have AST "effectively" come from CNJ anyway (though not locking out non-CNJs who want to just pick it up at level 30), and not make picking up AST feel like a step backwards. And given the quests are ALREADY in ARR zones, it makes sense, like how you can pick up the GNB quest in Gridania at level 60.

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The only downside I can think of is that it might not work for DRK and MCH (Frey being decidedly an Ishgard thing and...I don't remember MCH, but I think it was somewhat, too?), so doing this for only AST might seem a bit weird.

But it's also pretty simple to do, relatively speaking, and would make AST much more accessible for players that are starting the game and really want it as their Healer Job.