I think Ruhi was really weak or hasn't attained her full powers during the time of the attack. I remember Vikrant saying something like that to her and that's why he stopped her from fighting with the men. Maybe that's why she needed Shivji to give her a new face. Shivanya and Shesha were already very powerful naagins and were planning their revenge for quite some time. But Ruhi's case is different.
I agree that the thandav was not upto the mark. Mouni used to slay the thandav. But it's OK. Not everyone is good in everything.
Regarding the Ishqbaaz dialogue copying, all these people keep copying one thing or the other from each other's serials. Not a big thing. It's not like they used to show everything original in the previous seasons.
I agree with the portrait thing. How come Ruhi's new face i.e., Vish's portrait is hanging there. I thought they are all old portraits of naags and naagins who are at least a 100 years old. So how come the new chehra's portrait is also present there??