I reckon that the only way we could know for certain what is Jordan and what is Sanderson would be to see Jordan's notes. Without having seen that, it is impossible to be certain. For instance, saying that Jordan wrote a scene in a more believable way could easily come down to bias against Sanderson, even unconscious bias, and not necessarily poor technique.
As for the dumb-ing down; I disagree. Sanderson does hit you over the head a bit; leads you by the nose; whatever you want to call it; but I don't think he purposely makes a character look bad to make one look good.
Rand vs Egwene in the tower. Rand is one of the most powerful ta'vern - ever - and the Dragon besides. He walks into the tower, uninvited, without being threatened, cajoled, manipulated etc, without an armed guard, politely asks to see the Amyrlin, and calmly waits for an audience. Now that must have scared the willies out of the Aes Sedai, who are so used to threatening, cajoling, manipulating etc that someone who comes along and does what they want without any of that must leave them a bit...deflated. It's like going out with the intention of starting a rip-roaring debate in which you expect to have to drag people kicking and screaming to your soapbox; except when you arrive, everyone is already there, calmly sitting and waiting for you. That'll take the wind out of you. It'll also scare you. You'd wonder what these people know that you don't. Then they announce they they are going to have the debate some place else, and just walk off. That makes you look stupid, because in reality they have completely outmaneuvered you. It's classic shock-and-awe. Rand takes the initiative right out of the Aes Sedai's hands by doing the last thing they would possibly expect him to do, then acting in a manner that they would not expect him to, then making an announcement that he's intending to do the last thing anybody, anywhere would expect him to do - an announcement that stuns them into silence - and then leaves before they can collect their wits. The sheer boldness of it shocks the Aes Sedai into inaction. Beautifully, neatly done. And none of it down to contrivance.
You can make much the same argument regarding all of the other cases.
Anyway, those're my two cents.