I'd say you're given the opposite of solid reasons to explore. Look at the whole Zorru thing, Lae'zel gets the patrol's position straight up pointed to her on her map. Why. Just keep it vague in dialogue, highlight the whole area instead of giving me a pointer in gameplay, and suddenly i'm no longer going out of my way to get Karlach's quest.
Ethel and the east section are a bit better because one could naturally stumble on her and the brothers while trying to avoid the goblin ambush in the settlement, but the only real story reason to venture that way, other than playing an entirely trusting character who confides in random old women, is the whole Khaga situation, which isn't really all that overt.
As for the Underdark, i think that's just iffy level design. Why place the cool optional area (tower) in the easily accessible lower left corner, the map's exit (duergars and boat) in the middle, and the only piece of story-relevant content, which also gives a really compelling reason to explore the cool option area, in the upper parts (myconid village and 'good' mindflayer).
Obviously none of the above would be issues if it wasn't for the plot's underlying urgency, and hell if i tune that big detail out the exploration feels very BG-like especially in the Underdark. But since urgency is a thing, i believe that approach should be most defintely sacrificed for a cleaner and more streamlined level design, at least until we're straight up told the tadpoles won't act out at any moment.
lol, mate
1. If you approach the githyanki first you can go through the blighted village full of hostile goblins or jump across the river see the gnolls/hyenas and follow the bridge. This leads directly to the tollhouse and the Karlach quest. I specifically didn't say the game funnels you into every quest or every house. That would be bad design. Furthermore you go under the bridge leading to the githyanki, which leads you to the gnoll encounter, which might lead you to the zhentarim. The burning inn is on the way anyway. Then you get to the githyanki. I think you're getting confused between a suggestion of a story reason to explore and a divine mandate to do so
2. Yes you can meet Ethel on the road, even miss her in the camp. But if you do talk to her the first thing she does is give you a potion of GREATER healing for free and tells you she's a healer of sorts. I would say you would have to be actually UNtrusting not to take a chance given this is precisely what you have all agreed you need (Shadowheart doesn't trust her). Furthermore if you speak with her as Astarion, Shadowheart or Wyl, you are specifically alerted to the fact this is no ordinary woman. But again, no-one is saying you are forced to take any of these options, merely that the options exist
3. You are specifically pointed to this area. The mindflayer says he needs ingredients that can help you and the hobgoblin has mentioned the owner of the tower, an acquaintance of theirs, collects herbs/fungi. Even on the ground floor you can see this might be a suitable place to get the ingredients. Furthermore there are multiple ways to get to the UD, one of which lands you more or less outside the door.
It's perfectly fine to have an opinion on the urgency of the story, it is a subjective experience that no-one can take away from anyone after all. And not everyone will play the same character or speak to the same npcs after all. But they've set it up so if you rest twice, speak to the dead drow and the true soul (all of which should happen before you have to choose which direction to take) then the fact that you aren't changing is yet another thing to investigate. Also the fact that they have gated a lot of the companion scenes behind resting shows that as a character you have probably come to terms with the fact that however long you've got, it's longer than the usual 7 days.
It is okay to think the plot should be more urgent. I think to be honest though they have to balance that with exploring (it is a videogame after all). I imagine some people don't think they've got that right and some do.
I don't understand your first point. You're told where the githyanki patrol is and it's pointed out in the map. Straight, village, bridge, left. I didn't mention the gnolls precisely because they're on the way, just like the inn is, but for Karlach you just have to willingly go the wrong way.
Don't get your second point either. At the end of the day i said what you said, which is that there isn't any real story reason to explore the swamp other than one dialogue with Ethel and the situation at the grove.
As for your third... same. What i said is that it makes no sense for the mindflayer to be placed in a less accesible part of the map than that of the optional area it sends you to, and that the area exit sitting in the middle of it all makes just as much sense.
I also don't see how the badly implemented rest/dialogue system is anything more than a case of ludonarrative dissonance. To get every dialogue available you gotta rest twice before reaching the grove(SH+Astarion's camping dialogues, then Gale's mirror scene), twice around the grove(at least one SH dialogue and then Raphael), once to get Astarion's reveal, thrice if you get all the dreams, and so on and so forth.
So, about two/three weeks worth of rests to explore a relatively small area while you're constantly reminded that you might just turn at any moment. Or maybe you won't. No hurry. It's not like we're reminded by every npc/companion, and indeed shown in one of the first scenes in the game, that the situation's pretty FUBAR.
This to say, it's not my opinion that the plot should be more urgent, that's all Larian, and neither do i believe that the areas should be gimped. What i'd like is for the latters to make sense with the former, and that until the urgency's reduced. All it takes, like i said, is for the level design to be a bit cleaner.
For example, roughly keep the Underdark as it is, with the encounters spread all over and the 'main' entrances at the bottom(Hag's lair and goblin's fort), but move the tower and beach at the upper corners with the myconid village more to the middle. Slide Karlach a bit west, maybe above the gnolls or something. That way i'm still exploring, i'm still getting reward for exploring, but doesn't clash as badly with the over-reaching story.