I've been saying for a while that he's a lame duck; what was funny to me was how similar his behavior is to Lanfear's so it's fitting that you noted how similar they are. Very poor emotional control on his part - he's ripe to be duped and used as a tool, just as Sammael was, so it is unsurprising that Moridin leads him by the nose.

As for Mesaana, Graendal had an entertaining assessment of her: a second-rate Chosen, who only recently could be said to be fully committed.

The only suspicious part was that they thought Semirhage might reveal things: this was completely at odds with what he know of her capture during the Age of Legends.

I'm suspicious mainly because it is possible that Demandred and Mesaana put on an act in front of Graendal and Moriding; they seemed to parade their personality foibles in front of the other two. Mesaana's behavior is also contrary to what we've seen before - she knows exactly what Aes Sedai are capable of, yet she seems to be stronger than Moghedien. It seems to me that she showed an independent streak when she didn't go to the Cleansing that actually doesn't agree with this image of her as a begging supplicant. We're supposed to believe that she would not obey a direct order from the Dark One, but she was all for mounting a rescue for another Forsaken?

Perhaps in this desire for competence on the part of the protagonists and the antagonists, I'm giving them both too much credit, though, and they might truly be as stupid as they looked in that scene.