An unsupervised child in a candy store is the perfect way to describe Larian's writing style, not just in act 3 but throughout the game.
I think that from the very beginning the plot is just non-functional, pretty much. I'd say that from the openning cinematic, the plot was broken. If you asked me, to redo the plot from the ground up, the first major change would be to the beginning of the story. Instead of knowing we're tadpoled, we should have started by waking up in some randome settlement with no understanding of how we got there. Maybe being nursed to health by someone, maybe we were found in the wilderness. We could remember who we were, just have a blank space in our memory of how we got to where we were, as well as perhaps a chunk of time before our arrivial. Then act 1 would be exploring the town, doing adventures there and in the surrounding area, actually getting a feeling of being anchored in the setting and having a bit of agency in what's going on. As the story progresses we hear about the cult of the absolute and start having strange moments, hints at our altered abilities due to being tadpoled. We meet a couple of our would-be companions and things develop from there as we eventually discover that we've been tadpoled and what that means. Now instead of knowing we're on a ticking clock right away, it's something we discover later, and that creates a proper sense of escalation, but even then, by the time we discover it, it's been long enough that we know our change is weird and we don't feel quite as much pressure to rush, but we do still feel pressure. But we also aren't entirely aimless because we have the mystery of our lost memories to provide intrigue.
This plot could even still lead us to Moonrise and the shadow-cursed lands. Imagine if the town was far enough from the shadow curse to still be able to thrive, but close enough that stray undead from there were still an occasional problem. Like they had to be careful because they don't go more than a couple of months withouot dealing with some stray undead, and the location of the curse means that trade with Baldur's Gate, a city that could otherwise help them and make them more prosperous, is difficult to the point of generally being impractical. Just like that, the shadow-curse actually feels like something that hs impact on the world, not just a bizarrely isolated thing that's within reasonable travelling distance from a major city yet is entirely unmentioned within the city itself.
