[FULL GAME SPOILERS] Who were the Monsters?

[humanoid]

Where did I say anything about it not having a personality/consciousness?

Here is what you said:

I don't think every monster is supposed to be a person (that gets mentioned in the game).

Any existing monster HAS TO BE an existing character in the game (or, basically, in the scope of realm WAU operates), because WAU cannot create personality/character out of nothing, he is not even full-fledged AI himself.

Hence the appendix "(that gets mentioned in the game)".

So whatever monster you see in the game - has a base brain scan of someone. Whatever he turned into later because of such metamorphosis is another thing.

The game doesn't reveal that much about the WAU to lead to this assumption.

By your logic Akers would not be Akers anymore but rather replaced by a "brain scan of someone", not to mention the entire wildlife including the fish/deepsea creatures that attack you (if we're strictly talking about hostile lifeforms which I generally refer to as "monsters").

Fact is, we can only speculate what WAU's intentions are and how it spreads itself over Pathos-II with the structure gel.
Might be that it really takes over the host it wishes to "possess" by completely replacing its personality/consciousness with a brainscan of someone else, might also be that it just gradually alters the original host without using any existing brainscan, up to the point where it doesn't have any resemblence with the original anymore (in which case you would be wrong with your statement).
We can't say for sure but the way I experienced the game, I'm leaning more towards the latter.

Of course this debate only goes for monsters that already had a personality/consciousness before WAU affected them, thats why I made the distinction with the brackets.
"Empty shells" like robots controlled by humans or already dead bodies obviously need to be filled with an already existing brainscan, otherwise various beings in the game wouldn't be able to exist the way they are presented to us (Simon-2, Simon-3, Carl, Robin, etc).