You're absolutely right it would be the best ending for everyone.
Something I've been wanting to talk about awhile is how out of place the forced ending is compared to the rest of the game.
Think of it like this. You're the Emperor and the adventurers you've been helping want to free Orpheus. You're certain this will kill them, and you know you need an Illithid to use the stones to stop the Netherbrain.
If you leave, right now, you lose everything you've tried to achieve. The Netherbrain wins, and you have to eventually escape to try again, which might not even work because it seems like the brain planned on you escaping in the first place. Or... or you could wait 5 seconds to see what happens when Orpheus breaks free. If he's free and instantly tries to kill the party, or breaks the protection, then you're part of the hive mind anyway, it's no different than leaving ASAP. But if the party is right... Then everything is salvageable, you can still win the fight and claim your freedom.
This is where, in my personal opinion, the game cracks completely. Not because it's a bad game, not because the choice isn't meaningful, but the game design of freedom consistently clashes with artistic intent. From that recent interview, it's very clear that Larian had always intentioned the final outcome being 'Will you become a monster to be the hero?' or something a kin to that. So if that's the story they want to tell, this is the decision they came up with to give the player for that story. Yes there is a chunk of it before with illithid powers, becoming half-illithid, but this is the final nail in the coffin for that choice, for them to tell that story. But it falls a part so easily because everything leading up this can be handled in a plethora of different ways.
Ketheric Thorm, a person who's lived several live times, served three different gods, can be TALKED DOWN from his first half of the boss fight, letting Myrkul take over with his avatar. The goblin horde can be sided with, decimated, have their leaders assassinated, or ignored all together. Ethel can make a deal with you, force you to get the rewards AND save Mayrina, or not taking a deal and saving Mayrina. But the Emperor, is unable to wait all of 5 seconds for Orpheus to say "I hate you for what you did to me, but you're right. We need an Illithid, we need you."
To paraphrase something my friends once told me: "Sometimes you need to limit options to tell the story you want to tell." And for DMing D&D or TTRPGs in general, I cannot disagree with this more. Let them ruin my plans, let them make peace with the baddy. I might have a story in mind, but I'd rather they make the story themselves, instead of me telling them how it is.
That's not to say Larian is bad for this narrative decision. It's rather understandable to say "I made this, I want to talk about this concept, and I want the choice to be a difficult one." But this is just a crack in video games that offer freedom as much as possible. It clashes with artistic vision. We can have a game that offers as much choice as possible, and we can have an over arching story. But these concepts do not work well together when you are unwilling to move on a concept or question. Something has to break. And in this case, it's the players freedom to affect the story. No Persuasion check, no attempt, not even a side quest to get them to listen to us before hand regarding the whole subject.
I fully agree with this idea, and it's the ending I want most. But this is a crack from a game pushed to it's near limits of player freedom, while trying to have an artistic design. And while I am very much in the camp of "Forget your original design, let the players have their agency you've been giving them for 99% of the game (still holes here and there)", this is what they wanted to do, or something very much like this, for a very long time of development.
