I don't think only KP is responsible for all the crap in the show, Although script is responsibility of KP, there is a team for script development and more over they are always under influence of Director, PH and Channel.
If KP alone writing some crap then his team, director, PH and Channel should be able to identify the crap things so its not only KP's fault.
When TRP is low for any show, its PH and Channel who use to interfere in the script so as to introduce something interesting to audience so that TRP raises.