A sequel is expected to have the original cast as far as possible. The main cast of Bunty & Babli 2 where Abhisekh has been replaced for whatever reason can not be accepted in the first place. The film would have certainly done well had this element been taken care by Chopra. The poor response is due to such change.
Saif on the other hand is no doubt a fine actor, but does not fit fully into the shoes of Abhisekh Bachchan.