I didn't know any of the QH actors before I started watching the show and needless to say my first love is for characters and then for the actors. While we all agree that KSG brought Asad to life, he himself distanced himself from Asad for reasons best known only to him by slowly morphing into KSG towards end of his tenure and there was undisputed difference between Asad portrayed by him pre and post June 2013.
Asad portrayed by KSG pre June is phenomenal but I like Asad being portrayed by Raqeush compared to Asad portrayed by KSG post June, therefore, replacement was made easy on me by KSG. Story telling and execution is getting better these days and that too makes it more appealing than ZOYAAN days. Asad portrayed by KSG danced with Zoya before family on their engagement, therefore, PDA is more a character growth than out of character in my POV.
TRPs are driven by combination of multiple factors such as good story, execution, acting, looking the character, editing and more. Lead pair chemistry can be a major contributor but can't be the only contributor in the long run, chemistry need support of story and execution as well.
I am neither fan of KSG nor RV, I will continue to watch QH as far as characters and story is in a decent shape. Currently, the story is moving well and performances are decent and therefore the TRPs are decent as well. Volume of episodes doesn't matter either 100 or 300 episodes, as far as CVs can hold interest of viewers they can run the show and as of now QH is still holding my interest, its just my personal opinion and similarly, you are entitled to your own.