The actors presented their views while Johar played the moderator at the Hindustan Times Leadership Summit held at the Taj Palace Hotel.
The actor, who has earned the 'perfectionist' tag with films like "Lagaan" and "Taare Zameen Par", said "cinema is going through a period of change and transformation".
"The late 70s and 80s, which was the disco era, was disappointing. I feel that from the late 80s onwards, there has been a gradual change. The definition of mainstream cinema is constantly changing and has widened now. The audience is also changing," Aamir said.
He, however, expressed disappointment over the trend of buying editorial space to garner positive reviews for upcoming movies and the rat race for soaring box office collections.
"The emphasis is more on box-office collection. I don't blame the audience but the filmmakers. Top filmmakers and actors are selecting scripts to bust the Rs.100 crore mark. They are scared to experiment. But cinema is an art. Film should allow creativity and the story should rule the heart," he said.
"There is also a trend of buying editorial space to promote films, which is wrong," he added.
karan Johar noted the criticisms by the actor, and said: "Filmmakers and production house is to blame... point noted."
Deepika, on the other hand, discussed how being an outsider from the film industry helped her grow and learn from her experiences.
"Not having a film background help me learn. Everything I have learnt is due to the time I have spent on the sets, through interactions and also by my mistakes. People talk about my successful films, but I have also given back to back flops. That phase has taught me a lot," she said.
The actress spoke about how Bollywood objectifies men too.
"Men are also objectified but we choose not to talk about it," she said.
The "Happy New Year" actress said she takes competition in a sporting spirit.
"Competition is good. It can be productive and we can learn a lot from it," she said. There were light moments during the session as well, with karan Johar asking Deepika how did Katrina Kaif perform in "Dhoom: 3".
The back story is Deepika is Ranbir Kapoor's former girlfriend and Katrina is rumoured to be dating the "Barfi!" actor. However, Deepika praised Katrina. "I think Katrina is one of the most hardworking persons I have ever met. And I think she was fantastic in 'Dhoom: 3'," she said.
Another light moment was when Aamir interrupted Karan Johar for the second time, and the filmmaker said: "He (Aamir) is the new moderator and I am here only for glamour."
Aamir also insisted that entertainment was not the end of their responsibility. "Our responsibility is to create heroes, motivate people, touch the good and make you glow. It is to infuse fresh oxygen into this country," he said.
