Agreed. If you read the Reddit post and the top comments the case is closed.
But back to the question about whether or not it's good writing. I enjoying solving mysteries but I don't like feeling that my efforts were futile. Once you put everything together the game should acknowledge that.
Does Larian employ good writers? I think so but the authors were given a difficult task on a tight timeline. Revise The Emperor so people can feel good about working with him. You have two emperors:
1. The rogue illithid that kept his personality and is a victim of xenophobic prejudice. It's a tragic necessity that he needs to hide his form and deceive others. Most adventurers would attack him on sight and so his deception is easily understood and forgiven.
2. The evil mastermind who is responsible for all the (non DU) misfortunes that the MC faces
Interpretation 1 is favored by people who identify with character in some manner. They too feel like the they need to hide their true selves from the world. Perhaps they are gay, trans or neurodiverse? Or perhaps they are just retail workers who need keep their contempt for their customers buried deep inside. This interpretation works well if you rely up and believe The Emperor's statements.
Interpretation 2 is the interpretation that best fits with the physical 'empirical' evidence in the game and with the statements made by the Elder Brain. Gortash has no incentive to author a deceptive diary and stash it in the most secure vault in Baldur's Gate; when he's speaking to himself he's telling the truth.
But the game cannot acknowledge the efforts taken by those who have solved the mystery without spoiling it for people who are happy with interpretation 1. Interpretation 2 makes people who accept interpretation 1 feel foolish. Interpretation 1 constructs fans of the emperor like the Nessa the displacer beast who can die without ever understanding that the person who protects and provides is actually manipulating her for his own ends.
If you've ever gotten into a discussion with people who strongly favor interpretation 1 you know that interpretation 2 offends them deeply.
So the writing is a flawed I don't think it is flawed because the writers lack talent. The flaw starts with the instructions given by the managers when the game was revised: tell two stories at the same time and make sure that people are happy with either interpretation. I couldn't have done it.
