He is surrounded by people because that is his Fort, and he has to stay there to become a Duke. Later on, if you revisit him, he will be in his own room with all traps prepared (mines and flamethrowers on the wall) and his most loyal guards only.
If you did not inform to return the Netherstone before coming up, all the guards will start attacking you. Going into his room is forbidden.
I really want to side with him because I like Lawful Evil character but then Larian did him so dirty.
I think you overlooked my point.
Orin can turn into those most trusted guards, but she can't turn into a Steel Watcher - and I don't think either Orin nor the PC will really care about "something being forbidden". It is emphasized many times that Orin is the second best Unholy Assassin, only second to the Dark Urge, and they are both elite. Gortash only has to stay there for the inauguration, after which point he can operate through political puppets - for being such a cunning politician, he for sure forgot to account for the one thing that he admitted as his weakness. It just simply makes him look like an idiot - and remember that when you start Act3, there is a cutscene where Orin literally walks up to Gortash and has him fooled, posing as a Sergeant, and could have killed him right then and there. Even for the inauguration itself, couldn't he conjure some sort of image? Create a mirror image (something akin to Gale's), and run a perfect script in tandem with the Grand Duke for the inauguration, and then quickly get off the stage.
Then you missed dialogue with Orin as well as some key details. She is not second best UA, in a Tav canon playthrough she actually kills DU, you can find the alabaster dragonborn's corpse in her bedchambers after killing her, and the alabaster dragonborn is the canonical DU's representation. It is only when you play DU that you can best her, and even when you play DU she reveals she got the drop on you and tortured you and tadpoled you, so you're not exactly the best UA if supposedly second best got the drop on you.
On top of that, while she can fool Gortash with shapeshifting, he already accounted for it. She cannot attack him because he bound both her and Ketheric's blades, this much Orin tells you when you probe her as to why she's requesting that you kill Gortash instead. Gortash is a former protege (really, more like indentured servant) of Raphael, he not only knows of Bane, but he has dabbled with a warlock background on top of his magic and mechanic contraptions. He used a magical binding so Orin cannot harm him, or she dies herself in the attempt. That's why she's pissed, because he knew both her and Ketheric would try to double cross him.
In fact, of the Chosen Three, only Gortash seems willing to keep his word. You can even roll and Insight check and confirm that when he offers to rule alongside you, he is telling the truth. Neither Orin or Ketheric have any intention of sharing rule, their alliance was a means to an end they were willing to betray at the earliest possible opening, and this is why Gortash created the binding pacts.
The only foolish thing about him is trusting you to not interfere with his plans. He overestimated his ability to smooth talk you and didn't really place any exit strategies in case you reneged. That part of weak writing is due to his cut content from Upper City, where he was obviously going to feature.
