That belief isn't correct. My friend lost 40kg without doing any cardio. Weight training and calorie deficit is more important in my opinion.
Cardio can help speed up fat loss for leaner individuals. Many top bodybuilder use cardio when they are looking to shred down to extremely low body fat percentages. I personally do 30-45 minutes of low intensity cardio a day for general health.
From what I've known and experience, cardio plays a huge role in shredding and maintaining weight. I also believe that cardio is the best way to lose weight and stay fit.