While I can understand EW feeling like the story was rushed, when it comes to Hydaelyn and Zodiark…
they are revealed to be primals. While Hydaelyn is more of a human-looking version, taking on many of Venat’s personality traits, she’s still just a primal. Venat gave herself to be the “heart” of Hydaelyn, and seemed to imbue the primal with her personality and motivations. Zodiark is a more bestial-looking primal, also created by the Ancients, and Elidibus was his heart. It might have a lot to do with the mental state of the summoners in this case. Zodiark was summoned by a panicked Convocation that was pretty much like “save us at any cost!” Whereas Venat had had some time afterwards to assess the situation and seemed more calm and focused on what she thought needed to be done at that point. But as far as “meeting Zodiark,” we met his heart, Elidibus, just as we met Hydaelyn’s, Venat. Zodiark was always a primal, a thought-form. Fandaniel “wore” him, much like Ysayla did Shiva in HW.
As for Garlemald, they were embroiled in a civil war for quite some time… though I agree it would’ve been cool to see it before it was reduced to rubble! lol we’ve had tiny glimpses of it, but usually it’s an NPC on a recon mission in a cutscene and not our character.