Literally every game since GSC has been the size of those two regions put together or larger.

Idk about that. Hoenn was pretty small and a third of the region was water. diamond/pearl region was about the size of kanto, pokemon white/black region was the same size as diamond and pearl. Maybe idk what I'm talking about but I'm pretty sure heartgold/soulsilver by far had the largest region.

You don't know what you're talking about. Hoenn, even without all the water, was the size of Kanto and Johto combined, and every region since has followed suit.

Kanto and Johto separately are only half-regions.

I want the region to feel more varied and less flat. My
biggest problem with 4th and 5th gen regions was just how boring they felt. The music, fine. But the layout felt more like someone took a Pokemon game making tool and added generic assets and then went BAM! Done.

Kanto was supposed to feel like modern urban Japan and it did well.
Johto was supposed to represent old Japan and I feel like it did a great job at that too.
Hoenn was very different and tropical.
Kalos was alright, it did a better job of showing a modern France than Unova did showing America.

But idk, 4 and 5 seemed very rushed (so did 6, probably moreso) so I just hope for the next game we get a region that feels new and fresh.

Also keep the ability to refight trainers. For some stupid reason you couldnt do that in B/W (could you also not do that in X/Y? I forget)

Quite the opposite. Sinnoh was by far the most fleshed out and thought out region so far. Only Unova really felt shallow geographically, and that was ammended a little in B2W2.

who else hates large cities in pokemon games??