My impression of Sword Coast Legends is that it wanted to turn being a GM into a game against the player. An asymmetrical battle of wits. I am hoping Larian does not emulate this.
I am hoping Larian tries to create an experience as close as possible to the established role of the GM in existing tabletop games such as D&D (ie, as a storyteller/facilitator).
Incorrect - SCL definitely tried to make (almost force) GM mode into being cooperative, storyteller/facilitator. It tried to appeal to very "beginning" GMs with no-experience and almost "hand-hold" them. It was like GM with training-wheels. You only had so much of a "threat" pool that you could "spend" creating monsters/traps on the fly so you didn't overwhelm the players.
I think it was a good attempt at trying to teach GM balance, and they also allowed GM playing without the "threat pool" training wheels if desired.
You could also "possess" any placed creature or NPC and move them, use their abilities, etc. A pretty decent GM mode actually - the core problem was the Fisher-Price "kiddie" adventure editor that handcuffed the storyteller/creator in what they were allowed to create. THAT was a huge miscalculation. Probably THE major cause of failure.