MitD XVIII: It's utterly unreasonable to expect us to have been paying any attention

[Kish]

I don't find this a particularly convincing argument, because there are two kinds of psionics. There's some creatures whose spell-like abilities are called psionics, and then there's the variant casting system. The former has been shown to be present in OOTS-world since #30, whereas it's clearly the latter whose existance Redcloak was uncertain about. And since the protean's psionic abilities are of the first kind, I don't think Redcloak's uncertainty about the existence of the second kind is particularly relevant.

Indeed. I would say: Redcloak didn't know about psionics, therefore no creature which is only able to do things he explicitly expected the creature in the darkness to do because of psionics is suitable.

...and the only thing he's ever indicated expecting the creature in the darkness to do, is "kill." And I am quite sure there is no powerful-with-or-without-psionics creature that absolutely needs psionics to do that.