(1) The introductory Irenicus dungeon was a mess of areas with crystals and Djinns, areas with prisoners, areas with Nymphs and forest, areas with clouds and other Djinns. It didn't make sense, it seemed as if they wanted to cram cool stuff into a small map. (2) In Amn, you could literally walk into a random tavern, manipulate a picture on a wall and directly step into a Lich's tomb. With no corridors, rooms or maze like secret passages in between. (3) The Underdark had a single map where Drow, Illithids, Duergar and Kuo Toa were crammed together, living almost next to each other.
-> all these issues are relatively minor in comparison, but they are also a bit sloppy. If you compare this to the undercity map of BG1 were you had a whole area of a destroyed city which basically only housed the final fight, there is a completely different design philosophy behind it.
(1) I partially agree, but it still makes way more sense than anything we see in BG3. Irenicus is an insanely powerful wizard, reasons for many/most prisoners being there are given IIRC. It is a high-level party dungeon (and in BG2, you do start as a reasonably high-level character), not unlike what you get in some D&D high-level P&P adventures. (2) Don't remember that at all, which Lich was that? (3) Drow had their own map, so did the Illithids and Kuo Toa, no? Then yeah, there was the in-between "hub" Underdark location which wasn't exactly huge, but as long as you have to "gather your party and venture forth" and travel between maps, you can at least pretend in your head-cannon these locations are reasonably far away from each other (even though IIRC there is no travel time). This is impossible with e.g. the druids/tieflings and goblins.
Also, BG2 is a 21 years old game, it is not unreasonable to expect BG3 being better and not _MUCH_ worse. I will absolutely agree that BG1 with it's many non-dense outdoor locations etc. definitely had a less theme-parky feeling than BG2.
And everything being crammed together isn't the only problem with BG3's world/location building (though it's a major one) - even if you consider only a specific location where people (or goblins...) live, there are major verisimilitude issues.
