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It feels like Game Freak exchanged Johto and Kanto's faux-openess and larger side areas for many more smaller ones, and leaving HMs as largely an exploration tool- you need Strength, Dive, and Waterfall within a very short time span in the story- was both merciful for progression and let you use them on your teams. It kind of hurt that there was nothing on the level of Cerulean Cave, but they went with quantity.
I would even say the silver lining of ORAS not having enough late-generation meat was realizing I had spent so much time with new periphery stuff that I had forgotten about all of the OLD periphery stuff. Of course ORAS should have been the one to GIVE us that mega dungeon- or least tack the various Mirage Island types together and give us a fewer bigger ones- but they, eh, spread the love again.