As Warren Spector once said, it's all illusion. Smoke and mirrors. When they did Deus Ex, which was meant to be the pinnacle in player agency at that time, they figured it was less about changing the narrative wholesale. As JC Denton in Deus Ex, you can't just say "Fuck it!", quit your job and book a flight to the moon, for a start. Eventually, you're going to see all the missions and one of the endings accounted for. This goes doubly so for games that have scripted narratives alongside to dialogue etc., rather than FULLY emergent ones, such as Dwarf Fortress. Eventually, everything that's gonna happen narrative wise, somebody had scripted after all (and in fact, lots of the most popular things to this day in Deus Ex are wholly scripted). That's smoke and mirrors right there.
Warren Spector argued it would be rather about providing moment to moment gameplay decisions that altered things, and let players solve stuff in their own way. Like BG3 does a lot of the time, individual quests included. Which actually NONE of the Inifinty Engine games allowed for, its quests are mostly completely linear in terms of how you solve them. They had their own strengths (or else I wouldn't replay BG1 every now and then). But that wasn't them. Fallout 1+2+Arcanum are far superior in that regard. And in the grander plot scheme of things, even the faction choice at the early stages of BG2 doesn't amount to anything by the end.
Pillars Of Eternity was the first Infinity Engine sort-ish game that was more open in that regard, at least for some quests... the fantastic Raedric questline early on being a prime example. However, here too it's all based on stuff the designers scripted. The way you can enter Raedric's fortress in a multitude of ways? It's not something you come up by yourself. Obisidan had to invidiually code those all into the game. The way you can betray allies even late into the questline? That's too dialogue options Obsidian specifically coded into the game. If you factor in systems such as AI, physics, object interaction, lighting, lines of sight/stealth etc. stuff becomes even more open, and players may solve stuff in ways you hadn't even anticipiated or accounted for (as was part of the goal in designing Deus Ex... or BG3).
Warren Spector, by chance, was also involved with Ultima/Origin Systems. And Ultima is Larian's platonic ideal (except for the world simulation aspects of it, such as night turning into day, every single NPC having a schedule going alongside to it, fairly natural landscapes with somewhat "realistic" scales and traveling times etc.). Unfortunately, BG3 in parts appears to be another case where all the best in choice&consequence is fairly frontloaded. E.g. despite their HUGE budgets, it's in parts the Vampire Bloodlines syndrome all over again... where it's clear Troika ran out of money eventually to keep the standards set by the early stages of the game. If only Larian had spent this huge amount of extra budget not on cinematics, but on further tuning emergent gameplay systems and further narrative branches...
But then, according to Swen, the game wouldn't have attracted as huge an audience and justified its budget. Just like Deus Ex didn't (and most of the games in a similar vein that came before and after it, whilst we're at it). In fact, going fully cinematic for BG3 was meant to draw more players, and apparently it helped to do just that. Bottom line: Cinematics are far too expensive and have to go! https://www.pcgamer.com/the-cinematic-bioware-style-rpg-is-dead-it-just-doesnt-know-it-yet/
In fact, going fully cinematic for BG3 was meant to draw more players, and apparently it helped to do just that. Bottom line: Cinematics are far too expensive and have to go! 
