Something to keep in mind which I didn't point out is that Gary Napper(?) the lead Alien designer said that the Alien had its behaviour and skill set stripped back to give us a chance.
Yeah, Gary had stated that the AI was stripped back - I hate to think how difficult it is normally.
Well, they said the exact same thing about the guards in the Thief reboot. in the end they were just really goofy and dumb, and I doubt they were at any point really 'smart' so much as plain overpowered. And I mean, it's not like game AI is actual intelligence. It's not difficult to make an enemy that you can't defeat, the hard part is making the behavior seem natural. Like in an FPS it would be simple enough to make the enemies run up to you and headshot you without fail, but that wouldn't be very fun or seem lifelike. Similarly here, when they say oh yeah the alien was super smart, I take that to mean it would just home in on you from way too far and feel unbalanced and unfair. They could make it attack you from the other side of the map if they wanted, the game tracks your location anyway so it would be simple to let the alien 'know' your position too and run there. Restricting its actions and reaction times while keeping it challenging enough, and making it act like a living thing is trickier, and then it's easy to end up with really goofy behavior too