Inspite of cheran's voluntary exit from the task, I don't think he is the worst bottom 2 performer.
Also, mugens contribution to murdering kavin, reshma, MV was significant. He could have been top 2 performer or even sandy for that matter.
Allowing to be killed is also fine, these killed people couldn't correlate and find out killer and not able to help investigation and didn't take effort to do so, but just because they were in sunlight (underneath umbrella), they want best performer. That is also acceptable to extent, but how come person like Sakshi who created such confusion at the end is best performer.