Monday night the fans were all over them and they went out and beat John Cena clean.
I agree with everything you said except this.
They beat Cena
relatively clean. Yeah, they didn't all jump him at once, there were no weapons or low blows employed, etc. But it took blind tags Cena didn't notice and attacks from behind to get any real advantage on him. And even after taking finisher after finisher, he was up moments after the match and ready to go.
Yes, they won. But they could have looked stronger. Not a huge deal, but it was six on one. Eventually, they should have just had Cena get worn out, unable to deal with fresh man after fresh man face to face.
As for a big mastermind being behind this, I'm against it. They're having no problem getting Nexus over on their own. Why insert someone who'll most likely only steal the spotlight from them and hinder the progress of a bankable star of the future? In addition, and I was saying this on another board the other day, Cena shouldn't turn to join Nexus because, frankly, WWE doesn't need to blow their load of every major dream angle they have left in the bank in order to make this major angle better. Book Nexus logically around Nexus and save Cena's turn so you can cash in at a later date. And yes, that means I don't want The Rock to return and face Nexus leader John Cena at SummerSlam.
As to the question of whether a Cena turn would logically work, I actually think it could. Nexus has been saying that their actions have meaning and aren't about Cena. In theory, their motivations could be so compelling to Cena that he would look to join up with them. Mastermind? I hope not. Future associate? I wouldn't be totally opposed to the notion with solid kayfabe logic. But I don't think it will help the angle.
Also... anyone but Triple H. Dear Lord.