So I guess I'm not doing too bad after all.
Those underground maps that
Dregnel
posted helped a lot, mostly to just remember where all of the underground areas were since I forgot to mark them all. Anyways, there's an absurd amount of chests in Sumeru city that count towards Avidya Forest completion %. I spent an hour or so climbing the tree and looking behind buildings, on roofs and stuff which got me like 8% just out of the city for that region. Lokapala I already had mostly completed just from farming Collei mushrooms. I spent a good bit of time today in the rainforest/rain tree area to the south, and got 14% completion progress just from that. Fucked up thing is that despite these totals being almost all ~80% or higher, I'm still at only 35% explored for the region according to the Reputation NPC.
I fully realize that 100% in an area doesn't mean you collected everything, but still, Sumeru is going to be absolutely massive by the time it's all out. And that doesn't count any subterranean areas or separate maps like Chasm or Dragonspine.
I gave Collei my level 90 Elegy of the End and she's even better at Dendro support now. I'm frankly surprised they gave us someone halfway decent as a freebie. I hope she reruns relatively soon on a new 5* banner so I can get some constellations. Dehya's banner would be ideal.
I also figured out what the hell Dori's role is, well, before C6 when she becomes a LOT better. She's basically a handmade support for Cyno (and Razor to a lesser extent if you wanted to build him Electro instead of Phys). I figured it was something like that, and after reading her passives and talents and Constellations, C6 Dori is the ideal support for Cyno, giving him near 100% uptime on Electro damage, healing, and ER, to keep him blasting his wolf form as soon as it's off cooldown. Kinda like the Kujou Sara to Shogun.